# Sokoban

Sokoban
You are encouraged to solve this task according to the task description, using any language you may know.

Demonstrate how to find a solution to a given Sokoban level. For the purpose of this task (formally, a PSPACE-complete problem) any method may be used. However a move-optimal or push-optimal (or any other -optimal) solutions is preferred.

Sokoban levels are usually stored as a character array where

• space is an empty square
• # is a wall
• @ is the player
• \$ is a box
• . is a goal
• + is the player on a goal
• * is a box on a goal
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
```

Sokoban solutions are usually stored in the LURD format, where lowercase l, u, r and d represent a move in that (left, up, right, down) direction and capital LURD represents a push.

Please state if you use some other format for either the input or output, and why.

## 11l

Translation of: Python
```[String] data
V nrows = 0
V px = 0
V py = 0
V sdata = ‘’
V ddata = ‘’

F init(board)
:data = board.split("\n")
:nrows = max(:data.map(r -> r.len))

V maps = [‘ ’ = ‘ ’, ‘.’ = ‘.’, ‘@’ = ‘ ’, ‘#’ = ‘#’, ‘\$’ = ‘ ’]
V mapd = [‘ ’ = ‘ ’, ‘.’ = ‘ ’, ‘@’ = ‘@’, ‘#’ = ‘ ’, ‘\$’ = ‘*’]

L(row) :data
V r = L.index
L(ch) row
V c = L.index
:sdata ‘’= maps[ch]
:ddata ‘’= mapd[ch]
I ch == ‘@’
:px = c
:py = r

F push(x, y, dx, dy, &data)
I :sdata[(y + 2 * dy) * :nrows + x + 2 * dx] == ‘#’
| data[(y + 2 * dy) * :nrows + x + 2 * dx] != ‘ ’
data = ‘’
R

data[y * :nrows + x] = ‘ ’
data[(y + dy) * :nrows + x + dx] = ‘@’
data[(y + 2 * dy) * :nrows + x + 2 * dx] = ‘*’

F is_solved(data)
L(i) 0 .< data.len
I (:sdata[i] == ‘.’) != (data[i] == ‘*’)
R 0B
R 1B

F solve()
V open = Deque([(:ddata, ‘’, :px, :py)])
V visited = Set([:ddata])
V dirs = ((0, -1, ‘u’, ‘U’), ( 1, 0, ‘r’, ‘R’),
(0,  1, ‘d’, ‘D’), (-1, 0, ‘l’, ‘L’))

L !open.empty
V (cur, csol, x, y) = open.pop_left()

L(di) dirs
V temp = copy(cur)
V (dx, dy) = (di[0], di[1])

I temp[(y + dy) * :nrows + x + dx] == ‘*’
push(x, y, dx, dy, &temp)
I temp != ‘’ & temp !C visited
I is_solved(temp)
R csol‘’di[3]
open.append((temp, csol‘’di[3], x + dx, y + dy))
E
I :sdata[(y + dy) * :nrows + x + dx] == ‘#’ | temp[(y + dy) * :nrows + x + dx] != ‘ ’
L.continue

temp[y * :nrows + x] = ‘ ’
temp[(y + dy) * :nrows + x + dx] = ‘@’

I temp !C visited
I is_solved(temp)
R csol‘’di[2]
open.append((temp, csol‘’di[2], x + dx, y + dy))

R ‘No solution’

V level =
|‘#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######’

init(level)
print(level"\n\n"solve())```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD
```

## Befunge

El código no es mío, sólo lo reproduzco.

```589*+0g"0"-25**689*+0g"0"-+50p     v # Sokoban - (c) Matthew Westcott 2000 # 03
83*>10p99*2->:00p10gg"x"-#v_v p01g<> ## # # # # # # # # # # # # # # # # # # #
<< ^  -1g01_^#!:     -1g00< > v      # # # # # # # # # # # # # # # # # # # # #
|-"8"_v#-"2":_v#-"6":_v#-"4":~<  <0 #
> 1  0>\$1+2  0>\$2+3%\0>\$1+3%40v  \$4<#
v -"0"gp04:-1+g<v:-1+g00p03:p <  \$p #
>#v_"X">30g40gv0>40g10g+1-g:"#"-!|0 #
0>"x" ^v1g00p<^1g04p03:_v#`\ "9"<0 #
v:g-2++<>0gg"X"-#v_"0">00 g10gp30g^ #
4#     ^g04g04g0<>" " ^v3<          #
>8*-#v_\$"o"   v ^1-1+g0< >00g30g30v #
#   >"0"-#v_v>          ^v01-2++g< #
^>#\$" " 0#<v>"@"50g1-50p^>g40g40gv #
v_^#!-"@"g-1+g04g01:-1+g03g00p-2++< #
>"0"50g1+50p>\10g40g+1-p30g02050g  |#
>,#-:#3_@#"a\rx#glg#lw\$Zhoo#Grqh\$"0<#
#####################################
########
#      #
# o@0o #
#    #
# o#
###  ###
#0  x 0#
########
```

## C

Long, long, long C99 code (plus GNU C nested functions). Doesn't output the movement keys, instead it animates the sequence for you. Solution is move optimized. For an even longer solution, see Sokoban/C.

```#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <assert.h>
#include <stdbool.h>

int w, h, n_boxes;
uint8_t *board, *goals, *live;

typedef uint16_t cidx_t;
typedef uint32_t hash_t;

/* board configuration is represented by an array of cell indices
of player and boxes */
typedef struct state_t state_t;

struct state_t { // variable length
hash_t h;
state_t *prev, *next, *qnext;
cidx_t c[];
};

size_t state_size, block_size = 32;

inline
state_t* newstate(state_t *parent) {
inline state_t* next_of(state_t *s) {
return (void*)((uint8_t*)s + state_size);
}

state_t *ptr;
block_size *= 2;
state_t *p = malloc(block_size * state_size);
assert(p);
p->next = block_root;
block_root = p;
ptr = (void*)((uint8_t*)p + state_size * block_size);
state_t *q;
for (q = next_of(p); q < ptr; p = q, q = next_of(q))
p->next = q;
p->next = NULL;
}

ptr->prev = parent;
ptr->h = 0;
return ptr;
}

inline
void unnewstate(state_t *p) {
}

enum { space, wall, player, box };

#define E "\033["
const char * const glyph1[] = { " ", "#", E"31m@"E"m", E"33m\$"E"m"};
const char * const glyph2[] = { E"32m."E"m", "#", E"32m@"E"m", E"32m\$"E"m"};
#undef E

// mark up positions where a box definitely should not be
void mark_live(const int c)
{
const int y = c / w, x = c % w;
if (live[c]) return;

live[c] = 1;
if (y > 1 && board[c - w] != wall && board[c - w * 2] != wall)
mark_live(c - w);
if (y < h - 2 && board[c + w] != wall && board[c + w * 2] != wall)
mark_live(c + w);
if (x > 1 && board[c - 1] != wall && board[c - 2] != wall)
mark_live(c - 1);
if (x < w - 2 && board[c + 1] != wall && board[c + 2] != wall)
mark_live(c + 1);
}

state_t *parse_board(const int y, const int x, const char *s)
{
w = x, h = y;
board = calloc(w * h, sizeof(uint8_t));
assert(board);
goals = calloc(w * h, sizeof(uint8_t));
assert(goals);
live  = calloc(w * h, sizeof(uint8_t));
assert(live);

n_boxes = 0;
for (int i = 0; s[i]; i++) {
switch(s[i]) {
case '#':	board[i] = wall;
continue;

case '.':	// fallthrough
case '+':	goals[i] = 1; // fallthrough
case '@':	continue;

case '*':	goals[i] = 1; // fallthrough
case '\$':	n_boxes++;
continue;
default:	continue;
}
}

const int is = sizeof(int);
state_size = (sizeof(state_t) + (1 + n_boxes) * sizeof(cidx_t) + is - 1)
/ is * is;

state_t *state = newstate(NULL);

for (int i = 0, j = 0; i < w * h; i++) {
if (goals[i]) mark_live(i);
if (s[i] == '\$' || s[i] == '*')
state->c[++j] = i;
else if (s[i] == '@' || s[i] == '+')
state->c[0] = i;
}

return state;
}

void show_board(const state_t *s)
{
unsigned char b[w * h];
memcpy(b, board, w * h);

b[ s->c[0] ] = player;
for (int i = 1; i <= n_boxes; i++)
b[ s->c[i] ] = box;

for (int i = 0; i < w * h; i++) {
printf((goals[i] ? glyph2 : glyph1)[ b[i] ]);
if (! ((1 + i) % w))
putchar('\n');
}
}

// K&R hash function
inline
void hash(state_t *s)
{
if (!s->h) {
register hash_t ha = 0;
cidx_t *p = s->c;
for (int i = 0; i <= n_boxes; i++)
ha = p[i] + 31 * ha;
s->h = ha;
}
}

state_t **buckets;
hash_t hash_size, fill_limit, filled;

void extend_table()
{
int old_size = hash_size;

if (!old_size) {
hash_size = 1024;
filled = 0;
fill_limit = hash_size * 3 / 4; // 0.75 load factor
} else {
hash_size *= 2;
fill_limit *= 2;
}

buckets = realloc(buckets, sizeof(state_t*) * hash_size);
assert(buckets);

// rehash
memset(buckets + old_size, 0, sizeof(state_t*) * (hash_size - old_size));

const hash_t bits = hash_size - 1;
for (int i = 0; i < old_size; i++) {
buckets[i] = NULL;
const int j = head->h & bits;
}
}
}

state_t *lookup(state_t *s)
{
hash(s);
state_t *f = buckets[s->h & (hash_size - 1)];
for (; f; f = f->next) {
if (//(f->h == s->h) &&
!memcmp(s->c, f->c, sizeof(cidx_t) * (1 + n_boxes)))
break;
}

return f;
}

{
if (lookup(s)) {
unnewstate(s);
return false;
}

if (filled++ >= fill_limit)
extend_table();

hash_t i = s->h & (hash_size - 1);

s->next = buckets[i];
buckets[i] = s;
return true;
}

bool success(const state_t *s)
{
for (int i = 1; i <= n_boxes; i++)
if (!goals[s->c[i]]) return false;
return true;
}

state_t *move_me(state_t *s, const int dy, const int dx)
{
const int y = s->c[0] / w;
const int x = s->c[0] % w;
const int y1 = y + dy;
const int x1 = x + dx;
const int c1 = y1 * w + x1;

if (y1 < 0 || y1 > h || x1 < 0 || x1 > w
|| board[c1] == wall)
return NULL;

int at_box = 0;
for (int i = 1; i <= n_boxes; i++) {
if (s->c[i] == c1) {
at_box = i;
break;
}
}

int c2;
if (at_box) {
c2 = c1 + dy * w + dx;
if (board[c2] == wall || !live[c2])
return NULL;
for (int i = 1; i <= n_boxes; i++)
if (s->c[i] == c2) return NULL;
}

state_t *n = newstate(s);
memcpy(n->c + 1, s->c + 1, sizeof(cidx_t) * n_boxes);

cidx_t *p = n->c;
p[0] = c1;

if (at_box) p[at_box] = c2;

// leet bubble sort
for (int i = n_boxes; --i; ) {
cidx_t t = 0;
for (int j = 1; j < i; j++) {
if (p[j] > p[j + 1])
t = p[j], p[j] = p[j+1], p[j+1] = t;
}
if (!t) break;
}

return n;
}

state_t *next_level, *done;

bool queue_move(state_t *s)
{
return false;

if (success(s)) {
puts("\nSuccess!");
done = s;
return true;
}

s->qnext = next_level;
next_level = s;
return false;
}

bool do_move(state_t *s)
{
return     queue_move(move_me(s,  1,  0))
|| queue_move(move_me(s, -1,  0))
|| queue_move(move_me(s,  0,  1))
|| queue_move(move_me(s,  0, -1));
}

void show_moves(const state_t *s)
{
if (s->prev)
show_moves(s->prev);
usleep(200000);
printf("\033[H");
show_board(s);
}

int main()
{
state_t *s = parse_board(

#define BIG 0

#if BIG == 0
8, 7,
"#######"
"#     #"
"#     #"
"#. #  #"
"#. \$\$ #"
"#.\$\$  #"
"#.#  @#"
"#######"

#elif BIG == 1
5, 13,
"#############"
"#  #        #"
"# \$\$\$\$\$\$\$  @#"
"#.......    #"
"#############"

#elif BIG == 2
5, 13,
"#############"
"#... #      #"
"#.\$\$\$\$\$\$\$  @#"
"#...        #"
"#############"

#else
11, 19,
"    #####          "
"    #   #          "
"    #   #          "
"  ### #\$##         "
"  #      #         "
"### #\$## #   ######"
"#   # ## #####   .#"
"# \$   \$         ..#"
"##### ### #@##   .#"
"    #     #########"
"    #######        "
#endif
);

show_board(s);
extend_table();
queue_move(s);
for (int i = 0; !done; i++) {
printf("depth %d\r", i);
fflush(stdout);

if (!next_level) {
puts("no solution?");
return 1;
}
}

printf("press any key to see moves\n");
getchar(), puts("\033[H\033[J");
show_moves(done);

#if 0
free(buckets);
free(board);
free(goals);
free(live);

while (block_root) {
void *tmp = block_root->next;
free(block_root);
block_root = tmp;
}
#endif

return 0;
}
```

## C#

```using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SokobanSolver
{
public class SokobanSolver
{
private class Board
{
public string Cur { get; internal set; }
public string Sol { get; internal set; }
public int X { get; internal set; }
public int Y { get; internal set; }

public Board(string cur, string sol, int x, int y)
{
Cur = cur;
Sol = sol;
X = x;
Y = y;
}
}

private string destBoard, currBoard;
private int playerX, playerY, nCols;

SokobanSolver(string[] board)
{
nCols = board[0].Length;
StringBuilder destBuf = new StringBuilder();
StringBuilder currBuf = new StringBuilder();

for (int r = 0; r < board.Length; r++)
{
for (int c = 0; c < nCols; c++)
{

char ch = board[r][c];

destBuf.Append(ch != '\$' && ch != '@' ? ch : ' ');
currBuf.Append(ch != '.' ? ch : ' ');

if (ch == '@')
{
this.playerX = c;
this.playerY = r;
}
}
}
destBoard = destBuf.ToString();
currBoard = currBuf.ToString();
}

private string Move(int x, int y, int dx, int dy, string trialBoard)
{

int newPlayerPos = (y + dy) * nCols + x + dx;

if (trialBoard[newPlayerPos] != ' ')
return null;

char[] trial = trialBoard.ToCharArray();
trial[y * nCols + x] = ' ';
trial[newPlayerPos] = '@';

return new string(trial);
}

private string Push(int x, int y, int dx, int dy, string trialBoard)
{

int newBoxPos = (y + 2 * dy) * nCols + x + 2 * dx;

if (trialBoard[newBoxPos] != ' ')
return null;

char[] trial = trialBoard.ToCharArray();
trial[y * nCols + x] = ' ';
trial[(y + dy) * nCols + x + dx] = '@';
trial[newBoxPos] = '\$';

return new string(trial);
}

private bool IsSolved(string trialBoard)
{
for (int i = 0; i < trialBoard.Length; i++)
if ((destBoard[i] == '.')
!= (trialBoard[i] == '\$'))
return false;
return true;
}

private string Solve()
{
char[,] dirLabels = { { 'u', 'U' }, { 'r', 'R' }, { 'd', 'D' }, { 'l', 'L' } };
int[,] dirs = { { 0, -1 }, { 1, 0 }, { 0, 1 }, { -1, 0 } };
ISet<string> history = new HashSet<string>();

while (!open.Count.Equals(0))
{
Board item = open.First();
open.RemoveFirst();
string cur = item.Cur;
string sol = item.Sol;
int x = item.X;
int y = item.Y;

for (int i = 0; i < dirs.GetLength(0); i++)
{
string trial = cur;
int dx = dirs[i, 0];
int dy = dirs[i, 1];

// are we standing next to a box ?
if (trial[(y + dy) * nCols + x + dx] == '\$')
{
// can we push it ?
if ((trial = Push(x, y, dx, dy, trial)) != null)
{
// or did we already try this one ?
if (!history.Contains(trial))
{

string newSol = sol + dirLabels[i, 1];

if (IsSolved(trial))
return newSol;

open.AddLast(new Board(trial, newSol, x + dx, y + dy));
}
}
// otherwise try changing position
}
else if ((trial = Move(x, y, dx, dy, trial)) != null)
{
if (!history.Contains(trial))
{
string newSol = sol + dirLabels[i, 0];
open.AddLast(new Board(trial, newSol, x + dx, y + dy));
}
}
}
}
return "No solution";
}

public static void Main(string[] a)
{
string level = "#######," +
"#     #," +
"#     #," +
"#. #  #," +
"#. \$\$ #," +
"#.\$\$  #," +
"#.#  @#," +
"#######";
System.Console.WriteLine("Level:\n");
foreach (string line in level.Split(','))
{
System.Console.WriteLine(line);
}
System.Console.WriteLine("\nSolution:\n");
System.Console.WriteLine(new SokobanSolver(level.Split(',')).Solve());
}
}
}
```

Output:

```Level:

#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

Solution:

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## C++

### Set-based Version

Works with: C++11

This heavily abuses the STL, including some of the newer features like regex and tuples.

This performs a breadth-first search by moves, so the results should be a move-optimal solution.

```#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <regex>
#include <tuple>
#include <set>
#include <array>
using namespace std;

class Board
{
public:
vector<vector<char>> sData, dData;
int px, py;

Board(string b)
{
regex pattern("([^\\n]+)\\n?");
sregex_iterator end, iter(b.begin(), b.end(), pattern);

int w = 0;
vector<string> data;
for(; iter != end; ++iter){
data.push_back((*iter)[1]);
w = max(w, (*iter)[1].length());
}

for(int v = 0; v < data.size(); ++v){
vector<char> sTemp, dTemp;
for(int u = 0; u < w; ++u){
if(u > data[v].size()){
sTemp.push_back(' ');
dTemp.push_back(' ');
}else{
char s = ' ', d = ' ', c = data[v][u];

if(c == '#')
s = '#';
else if(c == '.' || c == '*' || c == '+')
s = '.';

if(c == '@' || c == '+'){
d = '@';
px = u;
py = v;
}else if(c == '\$' || c == '*')
d = '*';

sTemp.push_back(s);
dTemp.push_back(d);
}
}

sData.push_back(sTemp);
dData.push_back(dTemp);
}
}

bool move(int x, int y, int dx, int dy, vector<vector<char>> &data)
{
if(sData[y+dy][x+dx] == '#' || data[y+dy][x+dx] != ' ')
return false;

data[y][x] = ' ';
data[y+dy][x+dx] = '@';

return true;
}

bool push(int x, int y, int dx, int dy, vector<vector<char>> &data)
{
if(sData[y+2*dy][x+2*dx] == '#' || data[y+2*dy][x+2*dx] != ' ')
return false;

data[y][x] = ' ';
data[y+dy][x+dx] = '@';
data[y+2*dy][x+2*dx] = '*';

return true;
}

bool isSolved(const vector<vector<char>> &data)
{
for(int v = 0; v < data.size(); ++v)
for(int u = 0; u < data[v].size(); ++u)
if((sData[v][u] == '.') ^ (data[v][u] == '*'))
return false;
return true;
}

string solve()
{
set<vector<vector<char>>> visited;
queue<tuple<vector<vector<char>>, string, int, int>> open;

open.push(make_tuple(dData, "", px, py));
visited.insert(dData);

array<tuple<int, int, char, char>, 4> dirs;
dirs[0] = make_tuple(0, -1, 'u', 'U');
dirs[1] = make_tuple(1, 0, 'r', 'R');
dirs[2] = make_tuple(0, 1, 'd', 'D');
dirs[3] = make_tuple(-1, 0, 'l', 'L');

while(open.size() > 0){
vector<vector<char>> temp, cur = get<0>(open.front());
string cSol = get<1>(open.front());
int x = get<2>(open.front());
int y = get<3>(open.front());
open.pop();

for(int i = 0; i < 4; ++i){
temp = cur;
int dx = get<0>(dirs[i]);
int dy = get<1>(dirs[i]);

if(temp[y+dy][x+dx] == '*'){
if(push(x, y, dx, dy, temp) && (visited.find(temp) == visited.end())){
if(isSolved(temp))
return cSol + get<3>(dirs[i]);
open.push(make_tuple(temp, cSol + get<3>(dirs[i]), x+dx, y+dy));
visited.insert(temp);
}
}else if(move(x, y, dx, dy, temp) && (visited.find(temp) == visited.end())){
if(isSolved(temp))
return cSol + get<2>(dirs[i]);
open.push(make_tuple(temp, cSol + get<2>(dirs[i]), x+dx, y+dy));
visited.insert(temp);
}
}
}

return "No solution";
}
};

int main()
{
string level =
"#######\n"
"#     #\n"
"#     #\n"
"#. #  #\n"
"#. \$\$ #\n"
"#.\$\$  #\n"
"#.#  @#\n"
"#######";

Board b(level);

cout << level << endl << endl << b.solve() << endl;
return 0;
}
```

Output:

```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

### Unordered Set-based Version

Works with: C++11
Works with: Boost
Works with: GCC 4.6

```#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <tuple>
#include <array>
#include <map>
#include <boost/algorithm/string.hpp>
#include <boost/unordered_set.hpp>

using namespace std;

typedef vector<char> TableRow;
typedef vector<TableRow> Table;

struct Board {
Table sData, dData;
int px, py;

Board(string b) {
vector<string> data;
boost::split(data, b, boost::is_any_of("\n"));

size_t width = 0;
for (auto &row: data)
width = max(width, row.size());

map<char,char> maps = {{' ',' '}, {'.','.'}, {'@',' '},
{'#','#'}, {'\$',' '}},
mapd = {{' ',' '}, {'.',' '}, {'@','@'},
{'#',' '}, {'\$','*'}};

for (size_t r = 0; r < data.size(); r++) {
TableRow sTemp, dTemp;
for (size_t c = 0; c < width; c++) {
char ch = c < data[r].size() ? data[r][c] : ' ';
sTemp.push_back(maps[ch]);
dTemp.push_back(mapd[ch]);
if (ch == '@') {
px = c;
py = r;
}
}
sData.push_back(sTemp);
dData.push_back(dTemp);
}
}

bool move(int x, int y, int dx, int dy, Table &data) {
if (sData[y+dy][x+dx] == '#' || data[y+dy][x+dx] != ' ')
return false;

data[y][x] = ' ';
data[y+dy][x+dx] = '@';
return true;
}

bool push(int x, int y, int dx, int dy, Table &data) {
if (sData[y+2*dy][x+2*dx] == '#' || data[y+2*dy][x+2*dx] != ' ')
return false;

data[y][x] = ' ';
data[y+dy][x+dx] = '@';
data[y+2*dy][x+2*dx] = '*';
return true;
}

bool isSolved(const Table &data) {
for (size_t r = 0; r < data.size(); r++)
for (size_t c = 0; c < data[r].size(); c++)
if ((sData[r][c] == '.') != (data[r][c] == '*'))
return false;
return true;
}

string solve() {
boost::unordered_set<Table, boost::hash<Table>> visited;
visited.insert(dData);

queue<tuple<Table, string, int, int>> open;
open.push(make_tuple(dData, "", px, py));

vector<tuple<int, int, char, char>> dirs = {
make_tuple( 0, -1, 'u', 'U'),
make_tuple( 1,  0, 'r', 'R'),
make_tuple( 0,  1, 'd', 'D'),
make_tuple(-1,  0, 'l', 'L')
};

while (open.size() > 0) {
Table temp, cur = get<0>(open.front());
string cSol = get<1>(open.front());
int x = get<2>(open.front());
int y = get<3>(open.front());
open.pop();

for (int i = 0; i < 4; ++i) {
temp = cur;
int dx = get<0>(dirs[i]);
int dy = get<1>(dirs[i]);

if (temp[y+dy][x+dx] == '*') {
if (push(x, y, dx, dy, temp) &&
visited.find(temp) == visited.end()) {
if (isSolved(temp))
return cSol + get<3>(dirs[i]);
open.push(make_tuple(temp, cSol + get<3>(dirs[i]),
x+dx, y+dy));
visited.insert(temp);
}
} else if (move(x, y, dx, dy, temp) &&
visited.find(temp) == visited.end()) {
if (isSolved(temp))
return cSol + get<2>(dirs[i]);
open.push(make_tuple(temp, cSol + get<2>(dirs[i]),
x+dx, y+dy));
visited.insert(temp);
}
}
}

return "No solution";
}
};

int main() {
string level = "#######\n"
"#     #\n"
"#     #\n"
"#. #  #\n"
"#. \$\$ #\n"
"#.\$\$  #\n"
"#.#  @#\n"
"#######";

cout << level << endl << endl;
Board board(level);
cout << board.solve() << endl;
return 0;
}
```

## D

### Shorter Version

Translation of: C++

This version uses the queue defined in the Queue/Usage task.

```import std.string, std.typecons, std.exception, std.algorithm;
import queue_usage2; // No queue in Phobos 2.064.

const struct Board {
private enum El { floor = ' ', wall = '#', goal = '.',
box = '\$', player = '@', boxOnGoal='*' }
private alias CTable = string;
private immutable size_t ncols;
private immutable CTable sData, dData;
private immutable int playerx, playery;

this(in string[] board) immutable pure nothrow @safe
in {
foreach (const row; board) {
assert(row.length == board[0].length,
"Unequal board rows.");
foreach (immutable c; row)
assert(c.inPattern(" #.\$@*"), "Not valid input");
}
} body {
/*static*/ immutable sMap =
[' ':' ', '.':'.', '@':' ', '#':'#', '\$':' '];
/*static*/ immutable dMap =
[' ':' ', '.':' ', '@':'@', '#':' ', '\$':'*'];
ncols = board[0].length;

int plx = 0, ply = 0;
CTable sDataBuild, dDataBuild;

foreach (immutable r, const row; board)
foreach (immutable c, const ch; row) {
sDataBuild ~= sMap[ch];
dDataBuild ~= dMap[ch];
if (ch == El.player) {
plx = c;
ply = r;
}
}

this.sData = sDataBuild;
this.dData = dDataBuild;
this.playerx = plx;
this.playery = ply;
}

private bool move(in int x, in int y, in int dx,
in int dy, ref CTable data)
const pure nothrow /*@safe*/ {
if (sData[(y + dy) * ncols + x + dx] == El.wall ||
data[(y + dy) * ncols + x + dx] != El.floor)
return false;

auto data2 = data.dup;
data2[y * ncols + x] = El.floor;
data2[(y + dy) * ncols + x + dx] = El.player;
data = data2.assumeUnique; // Not enforced.
return true;
}

private bool push(in int x, in int y, in int dx,
in int dy, ref CTable data)
const pure nothrow /*@safe*/ {
if (sData[(y + 2 * dy) * ncols + x + 2 * dx] == El.wall ||
data[(y + 2 * dy) * ncols + x + 2 * dx] != El.floor)
return false;

auto data2 = data.dup;
data2[y * ncols + x] = El.floor;
data2[(y + dy) * ncols + x + dx] = El.player;
data2[(y + 2 * dy) * ncols + x + 2*dx] = El.boxOnGoal;
data = data2.assumeUnique; // Not enforced.
return true;
}

private bool isSolved(in CTable data)
const pure nothrow @safe @nogc {
foreach (immutable i, immutable d; data)
if ((sData[i] == El.goal) != (d == El.boxOnGoal))
return false;
return true;
}

string solve() pure nothrow /*@safe*/ {
bool[immutable CTable] visitedSet = [dData: true];

alias Four = Tuple!(CTable, string, int, int);
GrowableCircularQueue!Four open;
open.push(Four(dData, "", playerx, playery));

static immutable dirs = [tuple( 0, -1, 'u', 'U'),
tuple( 1,  0, 'r', 'R'),
tuple( 0,  1, 'd', 'D'),
tuple(-1,  0, 'l', 'L')];

while (!open.empty) {
//immutable (cur, cSol, x, y) = open.pop;
immutable item = open.pop;
immutable cur = item[0];
immutable cSol = item[1];
immutable x = item[2];
immutable y = item[3];

foreach (immutable di; dirs) {
CTable temp = cur;
//immutable (dx, dy) = di[0 .. 2];
immutable dx = di[0];
immutable dy = di[1];

if (temp[(y + dy) * ncols + x + dx] == El.boxOnGoal) {
if (push(x, y, dx, dy, temp) && temp !in visitedSet) {
if (isSolved(temp))
return cSol ~ di[3];
open.push(Four(temp, cSol ~ di[3], x + dx, y + dy));
visitedSet[temp] = true;
}
} else if (move(x, y, dx, dy, temp) && temp !in visitedSet) {
if (isSolved(temp))
return cSol ~ di[2];
open.push(Four(temp, cSol ~ di[2], x + dx, y + dy));
visitedSet[temp] = true;
}
}
}

return "No solution";
}
}

void main() {
import std.stdio, core.memory;
GC.disable; // Uses about twice the memory.

immutable level =
"#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######";

immutable b = immutable(Board)(level.splitLines);
writeln(level, "\n\n", b.solve);
}
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

Run-time about 0.55 seconds with DMD compiler, 0.49 with LDC2 compiler.

### Faster Version

Translation of: C

This code is not idiomatic D, it retains most of the style of the C version.

```import core.stdc.stdio: printf, puts, fflush, stdout, putchar;
import core.stdc.stdlib: malloc, calloc, realloc, free, alloca, exit;

enum Cell : ubyte { space, wall, player, box }
alias CellIndex = ushort;
alias Thash = uint;

/// Board configuration is represented by an array of cell
/// indices of player and boxes.
struct State { // Variable length struct.
Thash h;
State* prev, next, qNext;
CellIndex[0] c_;

CellIndex get(in size_t i) inout pure nothrow @nogc {
return c_.ptr[i];
}

void set(in size_t i, in CellIndex v) pure nothrow @nogc {
c_.ptr[i] = v;
}

CellIndex[] slice(in size_t i, in size_t j) pure nothrow @nogc return {
return c_.ptr[i .. j];
}
}

__gshared Cell[] board;
__gshared bool[] goals, live;
__gshared size_t w, h, nBoxes, stateSize, blockSize = 32;
__gshared State* blockRoot, blockHead, nextLevel, done;
__gshared State*[] buckets;
__gshared Thash hashSize, fillLimit, filled;

State* newState(State* parent) nothrow @nogc {
static State* nextOf(State *s) nothrow @nogc {
return cast(State*)(cast(ubyte*)s + stateSize);
}

State* ptr;
blockSize *= 2;
auto p = cast(State*)malloc(blockSize * stateSize);
if (p == null)
exit(1);

p.next = blockRoot;
blockRoot = p;
ptr = cast(State*)(cast(ubyte*)p + stateSize * blockSize);
for (auto q = nextOf(p); q < ptr; p = q, q = nextOf(q))
p.next = q;
p.next = null;
}

ptr.prev = parent;
ptr.h = 0;
return ptr;
}

void unNewState(State* p) nothrow @nogc {
}

/// Mark up positions where a box definitely should not be.
void markLive(in size_t c) nothrow @nogc {
immutable y = c / w;
immutable x = c % w;
if (live[c])
return;

live[c] = true;
if (y > 1 && board[c - w] != Cell.wall &&
board[c - w * 2] != Cell.wall)
markLive(c - w);
if (y < h - 2 && board[c + w] != Cell.wall &&
board[c + w * 2] != Cell.wall)
markLive(c + w);
if (x > 1 && board[c - 1] != Cell.wall &&
board[c - 2] != Cell.wall)
markLive(c - 1);
if (x < w - 2 && board[c + 1] != Cell.wall &&
board[c + 2] != Cell.wall)
markLive(c + 1);
}

State* parseBoard(in size_t y, in size_t x, in char* s) nothrow @nogc {
static T[] myCalloc(T)(in size_t n) nothrow @nogc {
auto ptr = cast(T*)calloc(n, T.sizeof);
if (ptr == null)
exit(1);
return ptr[0 .. n];
}

w = x, h = y;
board = myCalloc!Cell(w * h);
goals = myCalloc!bool(w * h);
live = myCalloc!bool(w * h);

nBoxes = 0;
for (int i = 0; s[i]; i++) {
switch(s[i]) {
case '#':
board[i] = Cell.wall;
continue;
case '.', '+':
goals[i] = true;
goto case;
case '@':
continue;
case '*':
goals[i] = true;
goto case;
case '\$':
nBoxes++;
continue;
default:
continue;
}
}

enum int intSize = int.sizeof;
stateSize = (State.sizeof +
(1 + nBoxes) * CellIndex.sizeof +
intSize - 1)
/ intSize * intSize;

auto state = null.newState;

for (CellIndex i = 0, j = 0; i < w * h; i++) {
if (goals[i])
i.markLive;
if (s[i] == '\$' || s[i] == '*')
state.set(++j, i);
else if (s[i] == '@' || s[i] == '+')
state.set(0, i);
}

return state;
}

/// K&R hash function.
void hash(State* s, in size_t nBoxes) pure nothrow @nogc {
if (!s.h) {
Thash ha = 0;
foreach (immutable i; 0 .. nBoxes + 1)
ha = s.get(i) + 31 * ha;
s.h = ha;
}
}

void extendTable() nothrow @nogc {
int oldSize = hashSize;

if (!oldSize) {
hashSize = 1024;
filled = 0;
fillLimit = hashSize * 3 / 4; // 0.75 load factor.
} else {
hashSize *= 2;
fillLimit *= 2;
}

auto ptr = cast(State**)realloc(buckets.ptr,
(State*).sizeof * hashSize);
if (ptr == null)
exit(6);
buckets = ptr[0 .. hashSize];
buckets[oldSize .. hashSize] = null;

immutable Thash bits = hashSize - 1;
foreach (immutable i; 0 .. oldSize) {
buckets[i] = null;
immutable j = head.h & bits;
}
}
}

State* lookup(State *s) nothrow @nogc {
s.hash(nBoxes);
auto f = buckets[s.h & (hashSize - 1)];
for (; f; f = f.next) {
if (s.slice(0, nBoxes + 1) == f.slice(0, nBoxes + 1))
break;
}

return f;
}

bool addToTable(State* s) nothrow @nogc {
if (s.lookup) {
s.unNewState;
return false;
}

if (filled++ >= fillLimit)
extendTable;

immutable Thash i = s.h & (hashSize - 1);

s.next = buckets[i];
buckets[i] = s;
return true;
}

bool success(in State* s) nothrow @nogc {
foreach (immutable i; 1 .. nBoxes + 1)
if (!goals[s.get(i)])
return false;
return true;
}

State* moveMe(State* s, in int dy, in int dx) nothrow @nogc {
immutable int y = s.get(0) / w;
immutable int x = s.get(0) % w;
immutable int y1 = y + dy;
immutable int x1 = x + dx;
immutable int c1 = y1 * w + x1;

if (y1 < 0 || y1 > h || x1 < 0 || x1 > w || board[c1] == Cell.wall)
return null;

int atBox = 0;
foreach (immutable i; 1 .. nBoxes + 1)
if (s.get(i) == c1) {
atBox = i;
break;
}

int c2;
if (atBox) {
c2 = c1 + dy * w + dx;
if (board[c2] == Cell.wall || !live[c2])
return null;
foreach (immutable i; 1 .. nBoxes + 1)
if (s.get(i) == c2)
return null;
}

auto n = s.newState;
n.slice(1, nBoxes + 1)[] = s.slice(1, nBoxes + 1);

n.set(0, cast(CellIndex)c1);

if (atBox)
n.set(atBox, cast(CellIndex)c2);

// Bubble sort.
for (size_t i = nBoxes; --i; ) {
CellIndex t = 0;
foreach (immutable j; 1 .. i) {
if (n.get(j) > n.get(j + 1)) {
t = n.get(j);
n.set(j, n.get(j + 1));
n.set(j + 1, t);
}
}
if (!t)
break;
}

return n;
}

bool queueMove(State *s) nothrow @nogc {
return false;

if (s.success) {
"\nSuccess!".puts;
done = s;
return true;
}

s.qNext = nextLevel;
nextLevel = s;
return false;
}

bool doMove(State* s) nothrow @nogc {
return s.moveMe( 1,  0).queueMove ||
s.moveMe(-1,  0).queueMove ||
s.moveMe( 0,  1).queueMove ||
s.moveMe( 0, -1).queueMove;
}

void showBoard(in State* s) nothrow @nogc {
static immutable glyphs1 = " #@\$", glyphs2 = ".#@\$";

auto ptr = cast(ubyte*)alloca(w * h * ubyte.sizeof);
if (ptr == null)
exit(5);
auto b = ptr[0 .. w * h];
b[] = cast(typeof(b))board[];

b[s.get(0)] = Cell.player;
foreach (immutable i; 1 .. nBoxes + 1)
b[s.get(i)] = Cell.box;

foreach (immutable i, immutable bi; b) {
putchar((goals[i] ? glyphs2 : glyphs1)[bi]);
if (!((1 + i) % w))
'\n'.putchar;
}
}

void showMoves(in State* s) nothrow @nogc {
if (s.prev)
s.prev.showMoves;
"\n".printf;
s.showBoard;
}

int main() nothrow @nogc {
// Workaround for @nogc.
alias ctEval(alias expr) = expr;

enum uint problem = 0;

static if (problem == 0) {
auto s = parseBoard(8, 7, ctEval!(
"#######"~
"#     #"~
"#     #"~
"#. #  #"~
"#. \$\$ #"~
"#.\$\$  #"~
"#.#  @#"~
"#######"));

} else static if (problem == 1) {
auto s = parseBoard(5, 13, ctEval!(
"#############"~
"#  #        #"~
"# \$\$\$\$\$\$\$  @#"~
"#.......    #"
"#############"));

} else static if (problem == 2) {
auto s = parseBoard(11, 19, ctEval!(
"    #####          "~
"    #   #          "~
"    #   #          "~
"  ### #\$##         "~
"  #      #         "~
"### #\$## #   ######"~
"#   # ## #####   .#"~
"# \$   \$         ..#"~
"##### ### #@##   .#"~
"    #     #########"~
"    #######        "));
} else {
asset(0, "Not present problem.");
}

s.showBoard;
extendTable;
s.queueMove;
for (int i = 0; !done; i++) {
printf("depth %d\r", i);
stdout.fflush;

if (!nextLevel) {
"No solution?".puts;
return 1;
}
}

done.showMoves;

version (none) { // Free all allocated memory.
buckets.ptr.free;
board.ptr.free;
goals.ptr.free;
live.ptr.free;

while (blockRoot) {
auto tmp = blockRoot.next;
blockRoot.free;
blockRoot = tmp;
}
}

return 0;
}
```

## Elixir

Works with: Elixir version 1.3
Translation of: Ruby
```defmodule Sokoban do
defp setup(level) do
{leng, board} = normalize(level)
{player, goal} = check_position(board)
board = replace(board, [{".", " "}, {"+", " "}, {"*", "\$"}])
lurd = [{-1, "l", "L"}, {-leng, "u", "U"}, {1, "r", "R"}, {leng, "d", "D"}]
dirs = [-1, -leng, 1, leng]
end

defp normalize(level) do
board = String.split(level, "\n", trim: true)
|> Enum.map(&String.trim_trailing &1)
leng  = Enum.map(board, &String.length &1) |> Enum.max
board = Enum.map(board, &String.pad_trailing(&1, leng)) |> Enum.join
{leng, board}
end

defp check_position(board) do
board = String.codepoints(board)
player = Enum.find_index(board, fn c -> c in ["@", "+"] end)
goal = Enum.with_index(board)
|> Enum.filter_map(fn {c,_} -> c in [".", "+", "*"] end, fn {_,i} -> i end)
{player, goal}
end

wall = String.replace(board, ~r/[^#]/, " ")
|> String.codepoints
|> Enum.with_index
|> Enum.into(Map.new, fn {c,i} -> {i,c} end)
corner = search_corner(wall, goal, dirs)
end

Enum.reduce(dirs, acc, fn dir,acc2 ->
if wall[pos+dir] == "#", do: acc2,
else: acc2 ++ check_side(wall, dirs, pos+dir, dir, goal, dead, [])
end)
end)
end

defp replace(string, replacement) do
Enum.reduce(replacement, string, fn {a,b},str ->
String.replace(str, a, b)
end)
end

defp search_corner(wall, goal, dirs) do
Enum.reduce(wall, [], fn {i,c},corner ->
if c == "#" or i in goal do
corner
else
case count_wall(wall, i, dirs) do
2 -> if wall[i-1] != wall[i+1], do: [i | corner], else: corner
3 -> [i | corner]
_ -> corner
end
end
end)
end

defp check_side(wall, dirs, pos, dir, goal, dead, acc) do
if wall[pos] == "#" or
count_wall(wall, pos, dirs) == 0 or
pos in goal do
[]
else
if pos in dead, do: acc, else: check_side(wall, dirs, pos+dir, dir, goal, dead, [pos|acc])
end
end

defp count_wall(wall, pos, dirs) do
Enum.count(dirs, fn dir -> wall[pos + dir] == "#" end)
end

defp push_box(board, pos, dir, route, goal, dead_zone) do
pos2dir = pos + 2 * dir
if String.at(board, pos2dir) == " " and not pos2dir in dead_zone do
board2 = board |> replace_at(pos,     " ")
|> replace_at(pos+dir, "@")
|> replace_at(pos2dir, "\$")
unless visited?(board2) do
if solved?(board2, goal) do
IO.puts route
exit(:normal)
else
queue_in({board2, pos+dir, route})
end
end
end
end

defp move_player(board, pos, dir) do
board |> replace_at(pos, " ") |> replace_at(pos+dir, "@")
end

defp replace_at(str, pos, c) do
{left, right} = String.split_at(str, pos)
{_, right} = String.split_at(right, 1)
left <> c <> right
# String.slice(str, 0, pos) <> c <> String.slice(str, pos+1..-1)
end

defp solved?(board, goal) do
Enum.all?(goal, fn g -> String.at(board, g) == "\$" end)
end

@pattern :sokoban_pattern_set
@queue   :sokoban_queue

Agent.start_link(fn -> MapSet.new end, name: @pattern)
Agent.start_link(fn -> :queue.new end, name: @queue)
end

defp visited?(board) do
Agent.get_and_update(@pattern, fn set ->
{board in set, MapSet.put(set, board)}
end)
end

defp queue_in(data) do
Agent.update(@queue, fn queue -> :queue.in(data, queue) end)
end

defp queue_out do
Agent.get_and_update(@queue, fn q ->
case :queue.out(q) do
{{:value, data}, queue} -> {data, queue}
x -> x
end
end)
end

def solve(level) do
{board, player, goal, lurd, dead_zone} = setup(level)
visited?(board)
queue_in({board, player, ""})
end

case queue_out do
{board, pos, route} ->
Enum.each(lurd, fn {dir,move,push} ->
case String.at(board, pos+dir) do
"\$" -> push_box(board, pos, dir, route<>push, goal, dead_zone)
" " -> board2 = move_player(board, pos, dir)
unless visited?(board2) do
queue_in({board2, pos+dir, route<>move})
end
_ -> :not_move    # wall
end
end)
_ ->
IO.puts "No solution"
exit(:normal)
end
end
end

level = """
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
"""
IO.puts level
Sokoban.solve(level)
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

luULLulDDurrrddlULrruLLrrUruLLLulD
```

## Go

Translation of: C++

Well, it started as a C++ translation, but turned out different. It's still the breadth-first set-based algorithm, but I dropped the sdata/ddata optimization and just maintained a single string as the board representation. Also dropped the code to handle non-rectangular boards, and probably some other stuff too.

```package main

import (
"fmt"
"strings"
)

func main() {
level := `
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######`
fmt.Printf("level:%s\n", level)
fmt.Printf("solution:\n%s\n", solve(level))
}

func solve(board string) string {
buffer = make([]byte, len(board))
width := strings.Index(board[1:], "\n") + 1
dirs := []struct {
move, push string
dPos       int
}{
{"u", "U", -width},
{"r", "R", 1},
{"d", "D", width},
{"l", "L", -1},
}
visited := map[string]bool{board: true}
open := []state{state{board, "", strings.Index(board, "@")}}
for len(open) > 0 {
s1 := &open[0]
open = open[1:]
for _, dir := range dirs {
var newBoard, newSol string
newPos := s1.pos + dir.dPos
switch s1.board[newPos] {
case '\$', '*':
newBoard = s1.push(dir.dPos)
if newBoard == "" || visited[newBoard] {
continue
}
newSol = s1.cSol + dir.push
if strings.IndexAny(newBoard, ".+") < 0 {
return newSol
}
case ' ', '.':
newBoard = s1.move(dir.dPos)
if visited[newBoard] {
continue
}
newSol = s1.cSol + dir.move
default:
continue
}
open = append(open, state{newBoard, newSol, newPos})
visited[newBoard] = true
}
}
return "No solution"
}

type state struct {
board string
cSol  string
pos   int
}

var buffer []byte

func (s *state) move(dPos int) string {
copy(buffer, s.board)
if buffer[s.pos] == '@' {
buffer[s.pos] = ' '
} else {
buffer[s.pos] = '.'
}
newPos := s.pos + dPos
if buffer[newPos] == ' ' {
buffer[newPos] = '@'
} else {
buffer[newPos] = '+'
}
return string(buffer)
}

func (s *state) push(dPos int) string {
newPos := s.pos + dPos
boxPos := newPos + dPos
switch s.board[boxPos] {
case ' ', '.':
default:
return ""
}
copy(buffer, s.board)
if buffer[s.pos] == '@' {
buffer[s.pos] = ' '
} else {
buffer[s.pos] = '.'
}
if buffer[newPos] == '\$' {
buffer[newPos] = '@'
} else {
buffer[newPos] = '+'
}
if buffer[boxPos] == ' ' {
buffer[boxPos] = '\$'
} else {
buffer[boxPos] = '*'
}
return string(buffer)
}
```
Output:
```level:
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
solution:
ulULLulDDurrrddlULrruLLrrUruLLLulD
```

```import Control.Monad (liftM)
import Data.Array
import Data.List (transpose)
import Data.Maybe (mapMaybe)
import qualified Data.Sequence as Seq
import qualified Data.Set as Set
import Prelude hiding (Left, Right)

data Field = Space | Wall | Goal
deriving (Eq)

data Action = Up | Down | Left | Right | PushUp | PushDown | PushLeft | PushRight

instance Show Action where
show Up        = "u"
show Down      = "d"
show Left      = "l"
show Right     = "r"
show PushUp    = "U"
show PushDown  = "D"
show PushLeft  = "L"
show PushRight = "R"

type Index = (Int, Int)
type FieldArray = Array Index Field
type BoxArray = Array Index Bool
type PlayerPos = Index
type GameState = (BoxArray, PlayerPos)
type Game = (FieldArray, GameState)

toField :: Char -> Field
toField '#' = Wall
toField ' ' = Space
toField '@' = Space
toField '\$' = Space
toField '.' = Goal
toField '+' = Goal
toField '*' = Goal

toPush :: Action -> Action
toPush Up    = PushUp
toPush Down  = PushDown
toPush Left  = PushLeft
toPush Right = PushRight
toPush n     = n

toMove :: Action -> Index
toMove PushUp    = ( 0, -1)
toMove PushDown  = ( 0,  1)
toMove PushLeft  = (-1,  0)
toMove PushRight = ( 1,  0)
toMove n = toMove \$ toPush n

-- Parse the string-based game board into an easier-to-use format.
-- Assume that the board is valid (rectangular, one player, etc).
parseGame :: [String] -> Game
parseGame fieldStrs = (field, (boxes, player))
where
width     = length \$ head fieldStrs
height    = length fieldStrs
bound     = ((0, 0), (width - 1, height - 1))
flatField = concat \$ transpose fieldStrs
charField = listArray bound flatField
field     = fmap toField charField
boxes     = fmap (`elem` "\$*") charField
player    = fst \$ head \$ filter (flip elem "@+" . snd) \$ assocs charField

add :: (Num a, Num b) => (a, b) -> (a, b) -> (a, b)
add (a, b) (x, y) = (a + x, b + y)

-- Attempt to perform an action, returning the updated game and adjusted
-- action if the action was legal.
tryAction :: Game -> Action -> Maybe (Game, Action)
tryAction (field, (boxes, player)) action
| field ! vec == Wall = Nothing
| boxes ! vec =
if boxes ! vecB || field ! vecB == Wall
then Nothing
else Just ((field, (boxes // [(vec, False), (vecB, True)], vec)),
toPush action)
| otherwise = Just ((field, (boxes, vec)), action)
where
actionVec = toMove action

-- Search the game for a solution.
solveGame :: Game -> Maybe [Action]
solveGame (field, initState) =
liftM reverse \$ bfs (Seq.singleton (initState, [])) (Set.singleton initState)
where
goals           = map fst \$ filter ((== Goal) . snd) \$ assocs field
isSolved st     = all (st !) goals
possibleActions = [Up, Down, Left, Right]

-- Breadth First Search of the game tree.
bfs :: Seq.Seq (GameState, [Action]) -> Set.Set GameState -> Maybe [Action]
bfs queue visited =
case Seq.viewl queue of
Seq.EmptyL -> Nothing
(game@(boxes, _), actions) Seq.:< queueB ->
if isSolved boxes
then Just actions
else
let newMoves = filter (flip Set.notMember visited . fst) \$
map (\((_, g), a) -> (g, a)) \$
mapMaybe (tryAction (field, game)) possibleActions
visitedB = foldl (flip Set.insert) visited \$
map fst newMoves
queueC   = foldl (Seq.|>) queueB \$
map (\(g, a) -> (g, a:actions)) newMoves
in bfs queueC visitedB

exampleA :: [String]
exampleA =
["#######"
,"#     #"
,"#     #"
,"#. #  #"
,"#. \$\$ #"
,"#.\$\$  #"
,"#.#  @#"
,"#######"]

main :: IO ()
main =
case solveGame \$ parseGame exampleA of
Nothing       -> putStrLn "Unsolvable"
Just solution -> do
mapM_ putStrLn exampleA
putStrLn ""
putStrLn \$ concatMap show solution
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## Java

Translation of C++ via D

Works with: Java version 7
```import java.util.*;

public class Sokoban {
String destBoard, currBoard;
int playerX, playerY, nCols;

Sokoban(String[] board) {
nCols = board[0].length();
StringBuilder destBuf = new StringBuilder();
StringBuilder currBuf = new StringBuilder();

for (int r = 0; r < board.length; r++) {
for (int c = 0; c < nCols; c++) {

char ch = board[r].charAt(c);

destBuf.append(ch != '\$' && ch != '@' ? ch : ' ');
currBuf.append(ch != '.' ? ch : ' ');

if (ch == '@') {
this.playerX = c;
this.playerY = r;
}
}
}
destBoard = destBuf.toString();
currBoard = currBuf.toString();
}

String move(int x, int y, int dx, int dy, String trialBoard) {

int newPlayerPos = (y + dy) * nCols + x + dx;

if (trialBoard.charAt(newPlayerPos) != ' ')
return null;

char[] trial = trialBoard.toCharArray();
trial[y * nCols + x] = ' ';
trial[newPlayerPos] = '@';

return new String(trial);
}

String push(int x, int y, int dx, int dy, String trialBoard) {

int newBoxPos = (y + 2 * dy) * nCols + x + 2 * dx;

if (trialBoard.charAt(newBoxPos) != ' ')
return null;

char[] trial = trialBoard.toCharArray();
trial[y * nCols + x] = ' ';
trial[(y + dy) * nCols + x + dx] = '@';
trial[newBoxPos] = '\$';

return new String(trial);
}

boolean isSolved(String trialBoard) {
for (int i = 0; i < trialBoard.length(); i++)
if ((destBoard.charAt(i) == '.')
!= (trialBoard.charAt(i) == '\$'))
return false;
return true;
}

String solve() {
class Board {
String cur, sol;
int x, y;

Board(String s1, String s2, int px, int py) {
cur = s1;
sol = s2;
x = px;
y = py;
}
}
char[][] dirLabels = {{'u', 'U'}, {'r', 'R'}, {'d', 'D'}, {'l', 'L'}};
int[][] dirs = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}};

Set<String> history = new HashSet<>();

while (!open.isEmpty()) {
Board item = open.poll();
String cur = item.cur;
String sol = item.sol;
int x = item.x;
int y = item.y;

for (int i = 0; i < dirs.length; i++) {
String trial = cur;
int dx = dirs[i][0];
int dy = dirs[i][1];

// are we standing next to a box ?
if (trial.charAt((y + dy) * nCols + x + dx) == '\$') {

// can we push it ?
if ((trial = push(x, y, dx, dy, trial)) != null) {

// or did we already try this one ?
if (!history.contains(trial)) {

String newSol = sol + dirLabels[i][1];

if (isSolved(trial))
return newSol;

open.add(new Board(trial, newSol, x + dx, y + dy));
}
}

// otherwise try changing position
} else if ((trial = move(x, y, dx, dy, trial)) != null) {

if (!history.contains(trial)) {
String newSol = sol + dirLabels[i][0];
open.add(new Board(trial, newSol, x + dx, y + dy));
}
}
}
}
return "No solution";
}

public static void main(String[] a) {
String level = "#######,#     #,#     #,#. #  #,#. \$\$ #,"
+ "#.\$\$  #,#.#  @#,#######";
System.out.println(new Sokoban(level.split(",")).solve());
}
}
```
`ulULLulDDurrrddlULrruLLrrUruLLLulD`

## Julia

Translation of: Go
```struct BoardState
board::String
csol::String
position::Int
end

function move(s::BoardState, dpos)
buffer = Vector{UInt8}(deepcopy(s.board))
if s.board[s.position] == '@'
buffer[s.position] = ' '
else
buffer[s.position] = '.'
end
newpos = s.position + dpos
if s.board[newpos] == ' '
buffer[newpos] = '@'
else
buffer[newpos] = '+'
end
String(buffer)
end

function push(s::BoardState, dpos)
newpos = s.position + dpos
boxpos = newpos + dpos
if s.board[boxpos] != ' ' && s.board[boxpos] != '.'
return ""
end
buffer = Vector{UInt8}(deepcopy(s.board))
if s.board[s.position] == '@'
buffer[s.position] = ' '
else
buffer[s.position] = '.'
end
if s.board[newpos] == '\$'
buffer[newpos] = '@'
else
buffer[newpos] = '+'
end
if s.board[boxpos] == ' '
buffer[boxpos] = '\$'
else
buffer[boxpos] = '*'
end
String(buffer)
end

function solve(board)
width = findfirst("\n", board[2:end])[1] + 1
dopt = (u = -width, l = -1, d = width, r = 1)
visited = Dict(board => true)
open::Vector{BoardState} = [BoardState(board, "", findfirst("@", board)[1])]
while length(open) > 0
s1 = open[1]
open = open[2:end]
for dir in keys(dopt)
newpos = s1.position + dopt[dir]
x = s1.board[newpos]
if x == '\$' || x == '*'
newboard = push(s1, dopt[dir])
if newboard == "" || haskey(visited, newboard)
continue
end
newsol = s1.csol * uppercase(string(dir))
if findfirst(r"[\.\+]", newboard) ==  nothing
return newsol
end
elseif x == ' ' || x == '.'
newboard = move(s1, dopt[dir])
continue
end
newsol = s1.csol * string(dir)
else
continue
end
open = push!(open, BoardState(newboard, newsol, newpos))
visited[newboard] = true
end
end
"No solution" # we should only get here if no solution to the sokoban
end

const testlevel = strip(raw"""
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######""")
println("For sokoban level:\n\$testlevel\n...solution is :\n\$(solve(testlevel))")
```
Output:
```
For sokoban level:
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
...solution is :
ulULLulDDurrrddlULrruLrUruLLLulD

```

## Kotlin

Translation of: Java
```// version 1.2.0

class Sokoban(board: List<String>) {
val destBoard: String
val currBoard: String
val nCols = board[0].length
var playerX = 0
var playerY = 0

init {
val destBuf = StringBuilder()
val currBuf = StringBuilder()
for (r in 0 until board.size) {
for (c in 0 until nCols) {
val ch = board[r][c]
destBuf.append(if (ch != '\$' && ch != '@') ch else ' ')
currBuf.append(if (ch != '.') ch else ' ')
if (ch == '@') {
playerX = c
playerY = r
}
}
}
destBoard = destBuf.toString()
currBoard = currBuf.toString()
}

fun move(x: Int, y: Int, dx: Int, dy: Int, trialBoard: String): String {
val newPlayerPos = (y + dy) * nCols + x + dx
if (trialBoard[newPlayerPos] != ' ') return ""
val trial = trialBoard.toCharArray()
trial[y * nCols + x] = ' '
trial[newPlayerPos] = '@'
return String(trial)
}

fun push(x: Int, y: Int, dx: Int, dy: Int, trialBoard: String): String {
val newBoxPos = (y + 2 * dy) * nCols + x + 2 * dx
if (trialBoard[newBoxPos] != ' ') return ""
val trial = trialBoard.toCharArray()
trial[y * nCols + x] = ' '
trial[(y + dy) * nCols + x + dx] = '@'
trial[newBoxPos] = '\$'
return String(trial)
}

fun isSolved(trialBoard: String): Boolean {
for (i in 0 until trialBoard.length) {
if ((destBoard[i] == '.') != (trialBoard[i] == '\$')) return false
}
return true
}

fun solve(): String {
data class Board(val cur: String, val sol: String, val x: Int, val y: Int)
val dirLabels = listOf('u' to 'U', 'r' to 'R', 'd' to 'D', 'l' to 'L')
val dirs = listOf(0 to -1, 1 to 0, 0 to 1, -1 to 0)
val history = mutableSetOf<String>()

while (!open.isEmpty()) {
val (cur, sol, x, y) = open.poll()
for (i in 0 until dirs.size) {
var trial = cur
val dx = dirs[i].first
val dy = dirs[i].second

// are we standing next to a box ?
if (trial[(y + dy) * nCols + x + dx] == '\$') {

// can we push it ?
trial = push(x, y, dx, dy, trial)
if (!trial.isEmpty()) {

// or did we already try this one ?
if (trial !in history) {
val newSol = sol + dirLabels[i].second
if (isSolved(trial)) return newSol
open.add(Board(trial, newSol, x + dx, y + dy))
}
}
} // otherwise try changing position
else {
trial = move(x, y, dx, dy, trial)
if (!trial.isEmpty() && trial !in history) {
val newSol = sol + dirLabels[i].first
open.add(Board(trial, newSol, x + dx, y + dy))
}
}
}
}
return "No solution"
}
}

fun main(args: Array<String>) {
val level = listOf(
"#######",
"#     #",
"#     #",
"#. #  #",
"#. \$\$ #",
"#.\$\$  #",
"#.#  @#",
"#######"
)
println(level.joinToString("\n"))
println()
println(Sokoban(level).solve())
}
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD
```

## Nim

Translation of: Kotlin

We have chosen to use a double queue (deque) instead of a linked list.

```import deques, sets, strutils

type

Sokoban = object
destBoard: string
currBoard: string
nCols: Natural
playerX: Natural
playerY: Natural

Board = tuple[cur, sol: string; x, y: int]

func initSokoban(board: openArray[string]): Sokoban =
result.nCols = board[0].len
for row in 0..board.high:
for col in 0..<result.nCols:
let ch = board[row][col]
result.destBoard.add if ch notin ['\$', '@']: ch else: ' '
result.currBoard.add if ch != '.': ch else: ' '
if ch == '@':
result.playerX = col
result.playerY = row

func move(sokoban: Sokoban; x, y, dx, dy: int; trialBoard: string): string =
let newPlayerPos = (y + dy) * sokoban.nCols + x + dx
if trialBoard[newPlayerPos] != ' ': return
result = trialBoard
result[y * sokoban.nCols + x] = ' '
result[newPlayerPos] = '@'

func push(sokoban: Sokoban; x, y, dx, dy: int; trialBoard: string): string =
let newBoxPos = (y + 2 * dy) * sokoban.nCols + x + 2 * dx
if trialBoard[newBoxPos] != ' ': return
result = trialBoard
result[y * sokoban.nCols + x] = ' '
result[(y + dy) * sokoban.nCols + x + dx] = '@'
result[newBoxPos] = '\$'

func isSolved(sokoban: Sokoban; trialBoard: string): bool =
for i in 0..trialBoard.high:
if (sokoban.destBoard[i] == '.') != (trialBoard[i] == '\$'): return false
result = true

func solve(sokoban: Sokoban): string =
var history: HashSet[string]
history.incl sokoban.currBoard
const Dirs = [(0, -1, 'u', 'U'), (1, 0, 'r', 'R'), (0, 1, 'd', 'D'), (-1, 0, 'l', 'L')]
var open: Deque[Board]

while open.len != 0:
let (cur, sol, x, y) = open.popFirst()
for dir in Dirs:
var trial = cur
let dx = dir[0]
let dy = dir[1]

# Are we standing next to a box?
if trial[(y + dy) * sokoban.nCols + x + dx] == '\$':
# Can we push it?
trial = sokoban.push(x, y, dx, dy, trial)
if trial.len != 0:
# Or did we already try this one?
if trial notin history:
let newSol = sol & dir[3]
if sokoban.isSolved(trial): return newSol
open.addLast (trial, newSol, x + dx, y + dy)
history.incl trial

else:
# Try to change position.
trial = sokoban.move(x, y, dx, dy, trial)
if trial.len != 0 and trial notin history:
let newSol = sol & dir[2]
open.addLast (trial, newSol, x + dx, y + dy)
history.incl trial

result = "no solution"

when isMainModule:

const Level = ["#######",
"#     #",
"#     #",
"#. #  #",
"#. \$\$ #",
"#.\$\$  #",
"#.#  @#",
"#######"]

echo Level.join("\n")
echo()
echo initSokoban(Level).solve()
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## OCaml

Translation of: Python

This uses a breadth-first move search, so will find a move-optimal solution.

```type dir = U | D | L | R
type move_t = Move of dir | Push of dir

let letter = function
| Push(U) -> 'U' | Push(D) -> 'D' | Push(L) -> 'L' | Push(R) -> 'R'
| Move(U) -> 'u' | Move(D) -> 'd' | Move(L) -> 'l' | Move(R) -> 'r'

let cols = ref 0
let delta = function U -> -(!cols) | D -> !cols | L -> -1 | R -> 1

let store = Hashtbl.create 251
let mark t = Hashtbl.replace store t ()
let marked t = Hashtbl.mem store t

let show ml =
List.iter (fun c -> print_char (letter c)) (List.rev ml); print_newline()

let gen_moves (x,boxes) bd =
let empty i = bd.(i) = ' ' && not (List.mem i boxes) in
let check l dir =
let dx = delta dir in
let x1 = x+dx in
if List.mem x1 boxes then (
if empty (x1+dx) then Push(dir) :: l else l
) else (
if bd.(x1) = ' ' then Move(dir) :: l else l
) in
(List.fold_left check [] [U; L; R; D])

let do_move (x,boxes) = function
| Push(d) -> let dx = delta d in
let x1 = x+dx in let x2 = x1+dx in
let rec shift = function
| [] -> failwith "shift"
| h :: t -> if h = x1 then x2 :: t else h :: shift t in
x1, List.fast_sort compare (shift boxes)
| Move(d) -> (x+(delta d)), boxes

let init_pos bd =
let p = ref 0 in
let q = ref [] in
let check i c =
if c = '\$' || c = '*' then q := i::!q
else if c = '@' then p := i in (
Array.iteri check bd;
(!p, List.fast_sort compare !q);
)

let final_box bd =
let check (i,l) c = if c = '.' || c = '*' then (i+1,i::l) else (i+1,l) in
List.fast_sort compare (snd (Array.fold_left check (0,[]) bd))

let array_of_input inp =
let r = List.length inp and c = String.length (List.hd inp) in
let a = Array.create (r*c) ' ' in (
for i = 0 to pred r do
let s = List.nth inp i in
for j = 0 to pred c do a.(i*c+j) <- s.[j] done
done;
cols := c; a)

let solve b =
let board = array_of_input b in
let targets = final_box board in
let solved pos = targets = snd pos in
let clear = Array.map (function '#' -> '#' | _ -> ' ') in
let bdc = clear board in
let q = Queue.create () in
let pos1 = init_pos board in
begin
mark pos1;
while not (Queue.is_empty q) do
let curr, mhist = Queue.pop q in
let moves = gen_moves curr bdc in
let check m =
let next = do_move curr m in
if not (marked next) then
if solved next then (show (m::mhist); exit 0)
else (mark next; Queue.add (next,m::mhist) q) in
List.iter check moves
done;
print_endline "No solution"
end;;

let level = ["#######";
"#     #";
"#     #";
"#. #  #";
"#. \$\$ #";
"#.\$\$  #";
"#.#  @#";
"#######"] in
solve level
```

Output:

`luULLulDDurrrddlULrruLLrrUruLLLulD`

## Perl

This performs simultaneous breadth first searches, starting from the initial state and various possible final states, and meeting somewhere in the middle.

On my laptop, which has a slow cpu and little memory, it can solve the basic puzzle in about a second, and a slightly harder one in about 50 seconds.

A slightly more basic version of this code, doing a single breadth first search, took twenty seconds for the basic puzzle, and was unable to solve the slightly harder one before I lost patience with it (about half an hour).

The meet-in-the-middle search uses massively less memory, but obviously more lines of code. Due to the way I alternate between forward and rearward computation, it's possible for the solution to be at most one step longer than the optimal one... but it would still be a valid solution. I could fix it, but at the cost of speed and memory.

```#!perl
use strict;
use warnings qw(FATAL all);
my @initial = split /\n/, <<'';
#############
#  #        #
# \$\$\$\$\$\$\$  @#
#.......    #
#############

#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

=for
space is an empty square
# is a wall
@ is the player
\$ is a box
. is a goal
+ is the player on a goal
* is a box on a goal
=cut

my \$cols = length(\$initial[0]);
my \$initial = join '', @initial;
my \$size = length(\$initial);
die unless \$size == \$cols * @initial;

sub WALL() { 1 }
sub PLAYER() { 2 }
sub BOX() { 4 }
sub GOAL() { 8 }

my %input = (
' ' => 0, '#' => WALL, '@' => PLAYER, '\$' => BOX,
'.' => GOAL, '+' => PLAYER|GOAL, '*' => BOX|GOAL,
);
my %output = reverse(%input);

sub packed_initial {
my \$ret = '';
vec( \$ret, \$_, 4 ) = \$input{substr \$initial, \$_, 1}
for( 0 .. \$size-1 );
\$ret;
}

sub printable_board {
my \$board = shift;
my @c = @output{map vec(\$board, \$_, 4), 0 .. \$size-1};
my \$ret = '';
while( my @row = splice @c, 0, \$cols ) {
\$ret .= join '', @row, "\n";
}
\$ret;
}

my \$packed = packed_initial();

my @udlr = qw(u d l r);
my @UDLR = qw(U D L R);
my @deltas = (-\$cols, +\$cols, -1, +1);

my %fseen;
INIT_FORWARD: {
\$initial =~ /(\@|\+)/ or die;
use vars qw(@ftodo @fnext);
@ftodo = (["", \$packed,  \$-[0]]);
\$fseen{\$packed} = '';
}

my %rseen;
INIT_REVERSE: {
my \$goal = \$packed;
vec(\$goal, \$ftodo[0][2], 4) -= PLAYER;
my @u = grep { my \$t = vec(\$goal, \$_, 4); \$t & GOAL and not \$t & BOX } 0 .. \$size-1;
my @b = grep { my \$t = vec(\$goal, \$_, 4); \$t & BOX and not \$t & GOAL } 0 .. \$size-1;
die unless @u == @b;
vec(\$goal, \$_, 4) += BOX for @u;
vec(\$goal, \$_, 4) -= BOX for @b;
use vars qw(@rtodo @rnext);
FINAL_PLACE: for my \$player (0 .. \$size-1) {
next if vec(\$goal, \$player, 4);
FIND_GOAL: {
vec(\$goal, \$player + \$_, 4) & GOAL and last FIND_GOAL for @deltas;
next FINAL_PLACE;
}
my \$a_goal = \$goal;
vec(\$a_goal, \$player, 4) += PLAYER;
push @rtodo, ["", \$a_goal, \$player ];
\$rseen{\$a_goal} = '';
#print printable_board(\$a_goal);
}
}

my \$movelen = -1;
my (\$solution);
MAIN: while( @ftodo and @rtodo ) {

FORWARD: {
my (\$moves, \$level, \$player) = @{pop @ftodo};
die unless vec(\$level, \$player, 4) & PLAYER;

for my \$dir_num (0 .. 3) {
my \$delta = \$deltas[\$dir_num];
my @loc = map \$player + \$delta * \$_, 0 .. 2;
my @val = map vec(\$level, \$_, 4), @loc;

next if \$val[1] & WALL or (\$val[1] & BOX and \$val[2] & (BOX|WALL));

my \$new = \$level;
vec(\$new, \$loc[0], 4) -= PLAYER;
vec(\$new, \$loc[1], 4) += PLAYER;
my \$nmoves;
if( \$val[1] & BOX ) {
vec(\$new, \$loc[1], 4) -= BOX;
vec(\$new, \$loc[2], 4) += BOX;
\$nmoves = \$moves . \$UDLR[\$dir_num];
} else {
\$nmoves = \$moves . \$udlr[\$dir_num];
}

next if exists \$fseen{\$new};
\$fseen{\$new} = \$nmoves;

push @fnext, [ \$nmoves, \$new, \$loc[1] ];

exists \$rseen{\$new} or next;
#print((\$val[1] & BOX) ? "Push \$UDLR[\$dir_num]\n" : "Fwalk \$udlr[\$dir_num]\n");
\$solution = \$new;
last MAIN;
}

last FORWARD if @ftodo;
use vars qw(*ftodo *fnext);
(*ftodo, *fnext) = (\@fnext, \@ftodo);
} # end FORWARD

BACKWARD: {
my (\$moves, \$level, \$player) = @{pop @rtodo};
die "<\$level>" unless vec(\$level, \$player, 4) & PLAYER;

for my \$dir_num (0 .. 3) {
my \$delta = \$deltas[\$dir_num];
# look behind and in front of the player.
my @loc = map \$player + \$delta * \$_, -1 .. 1;
my @val = map vec(\$level, \$_, 4), @loc;

# unlike the forward solution, we cannot push boxes
next if \$val[0] & (WALL|BOX);
my \$new = \$level;
vec(\$new, \$loc[0], 4) += PLAYER;
vec(\$new, \$loc[1], 4) -= PLAYER;
# unlike the forward solution, if we have a box behind us
# we can *either* pull it or not.  This means there are
# two "successors" to this board.
if( \$val[2] & BOX ) {
my \$pull = \$new;
vec(\$pull, \$loc[2], 4) -= BOX;
vec(\$pull, \$loc[1], 4) += BOX;
goto RWALK if exists \$rseen{\$pull};
my \$pmoves = \$UDLR[\$dir_num] . \$moves;
\$rseen{\$pull} = \$pmoves;
push @rnext, [\$pmoves, \$pull, \$loc[0]];
goto RWALK unless exists \$fseen{\$pull};
print "Doing pull\n";
\$solution = \$pull;
last MAIN;
}
RWALK:
next if exists \$rseen{\$new}; # next direction.
my \$wmoves = \$udlr[\$dir_num] . \$moves;
\$rseen{\$new} = \$wmoves;
push @rnext, [\$wmoves, \$new, \$loc[0]];
next unless exists \$fseen{\$new};
print "Rwalk\n";
\$solution = \$new;
last MAIN;
}

last BACKWARD if @rtodo;
use vars qw(*rtodo *rnext);
(*rtodo, *rnext) = (\@rnext, \@rtodo);
} # end BACKWARD
}

if( \$solution ) {
my \$fmoves = \$fseen{\$solution};
my \$rmoves = \$rseen{\$solution};
print "Solution found!\n";
print "Time: ", (time() - \$^T), " seconds\n";
print "Moves: \$fmoves \$rmoves\n";
print "Move Length: ", length(\$fmoves . \$rmoves), "\n";
print "Middle Board: \n", printable_board(\$solution);
} else {
print "No solution found!\n";
}
__END__
```
Output:
```Solution found!
Time: 51 seconds
Moves: lldlllllllluurDldRRRRRRRRuulD rdLLLLLLrrrrrurrrdLLLLLLLrrrruulDulDulDulDLLulD
Move Length: 76
Middle Board:
#############
#  #        #
#  \$\$\$\$\$@   #
#.......\$ \$ #
#############
```

On this particular puzzle, the branch factor for the different search directions were clearly quite different, as the forward search only did 29 moves, while the reverse search did 47 moves.

Although my code doesn't print out the actual final board, it would be easy enough to compute from the move list.

## Phix

Push-optimised, prunes (breadth-first) search space to reachable pushable-to-live boxes.
Fairly fast, but often produces same-push-tally but longer results than move-optimised.

```-- demo\rosetta\Sokoban.exw
integer w, h    -- (set from parsing the input grid)
sequence moves  --    "", as +/-w and +/-1 (udlr)
string live     --    "", Y if box can go there

function reachable(sequence pushes, string level)
integer p = find_any("@+",level)
string ok = repeat('N',length(level))
ok[p] = 'Y'
while true do
p = find('Y',ok)
if p=0 then exit end if
ok[p] = 'y'
for i=1 to length(moves) do
integer pn = p+moves[i]
if ok[pn]='N'
and find(level[pn]," .") then
ok[pn] = 'Y'
end if
end for
end while
for i=length(pushes)-1 to 1 by -2 do
if ok[pushes[i]-pushes[i+1]]!='y' then
pushes[i..i+1] = {}
end if
end for
return pushes
end function

function pushable(string level)
sequence res = {}
for i=1 to length(level) do
if find(level[i],"\$*") then
if  find(level[i-w]," .@+")
and find(level[i+w]," .@+") then
if live[i-w]='Y' then res &= {i,-w} end if
if live[i+w]='Y' then res &= {i,+w} end if
end if
if  find(level[i-1]," .@+")
and find(level[i+1]," .@+") then
if live[i-1]='Y' then res &= {i,-1} end if
if live[i+1]='Y' then res &= {i,+1} end if
end if
end if
end for
return reachable(res,level)
end function

function solve(string level)
atom t2 = time()+2
integer seen = new_dict()
sequence solution = "No solution.", partial = {}
sequence todo = {{level,partial,pushable(level)}}, pushes
while length(todo) do
sequence t1 = todo[1]
todo = todo[2..\$]
{level,partial,pushes} = t1
integer p = find_any("@+",level)
while length(pushes) do
integer {s,m} = pushes[1..2]
pushes = pushes[3..\$]
level[p] = " ."[find(level[p],"@+")]
level[s] = "@+"[find(level[s],"\$*")]
level[s+m] = "\$*"[find(level[s+m]," .")]
if getd_index(level,seen)=0 then
sequence np = partial&{s,m}
if not find('\$',level) then
solution = np
todo = {}
pushes = {}
exit
end if
setd(level,true,seen)
if time()>t2 then
printf(1,"working... (seen %d)\r",dict_size(seen))
t2 = time()+2
end if
todo = append(todo,{level,np,pushable(level)})
end if
level = t1[1] -- (reset)
end while
end while
destroy_dict(seen)
return solution
end function

procedure plays(string level, sequence solution)
-- This plays push-only solutions (see play() for lurd)
string res = level
integer p = find_any("@+",level)
for i=1 to length(solution) by 2 do
integer {s,m} = solution[i..i+1] m+=s
level[p] = " ."[find(level[p],"@+")]
level[s] = "@+"[find(level[s],"\$*")]
level[m] = "\$*"[find(level[m]," .")]
res &= level
p = s
end for
-- (replacing +0 with 1/2/3 may help in some cases)
puts(1,join_by(split(res,'\n'),h,floor(80/(w+2))+0))
end procedure

procedure mark_live(integer p, string level)
-- (idea cribbed from the C version)
if live[p]='N' then
live[p] = 'Y'
integer l = length(level)
if p-w*2>=1 and level[p-w]!='#' and level[p-w*2]!='#' then mark_live(p-w,level) end if
if p+w*2<=l and level[p+w]!='#' and level[p+w*2]!='#' then mark_live(p+w,level) end if
if p-2  >=1 and level[p-1]!='#' and level[p-2]  !='#' then mark_live(p-1,level) end if
if p+2  <=l and level[p+1]!='#' and level[p+2]  !='#' then mark_live(p+1,level) end if
end if
end procedure

function make_square(string level)
--
-- Sets {h, w, moves, live}, and returns an evened-out/rectangular level
--
if level[\$]!='\n' then level &= '\n' end if -- (for the display)
sequence lines = split(level,'\n')
h = length(lines)-1             -- set height (ignore trailing \n)
sequence ln = repeat(0,h)
for i=1 to h do
ln[i] = {length(lines[i]),i}
for j=1 to length(lines[i]) do
-- validate each line, why not
if not find(lines[i,j]," #.\$@*") then
crash("invalid input")
end if
end for
end for
ln = sort(ln)
w = ln[\$][1]+1                  -- set width (==longest, inc \n)
moves = {-w,+w,-1,+1}           -- and make these (udlr) legal ...
for i=1 to h do
integer {l,n} = ln[i], pad = w-1-l
if pad=0 then exit end if
lines[n] &= repeat(' ',pad) -- ... by evening up the "grid"
end for
level = join(lines,'\n')
live = join(repeat(repeat('N',w-1),h),'\n')
for p=1 to length(level) do
if find(level[p],".+*") then
mark_live(p,level)
end if
end for
return level
end function

constant input = """
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
"""

atom t0 = time()
string level = make_square(input)
sequence pushset = solve(level)
integer pop = length(pushset)/2
if string(pushset) then
puts(1,level)
printf(1,"%s\n",{pushset}) -- ("No Solution.")
else
printf(1,"solution of %d pushes (%s)\n",{pop,elapsed(time()-t0)})
plays(level,pushset)
end if
```
Output:

Note that a full solution in LURD format would show as 48 moves, as opposed to the move-optimal solutions of other entries of 34 moves, but both are 14 pushes.

```solution of 14 pushes (0.5s)
#######   #######   #######   #######   #######   #######   #######   #######
#     #   #     #   #     #   #     #   #     #   #     #   #     #   #     #
#     #   #     #   #   \$ #   #  \$@ #   # \$@  #   #\$@   #   #@    #   #     #
#. #  #   #. #\$ #   #. #@ #   #. #  #   #. #  #   #. #  #   #* #  #   #* #  #
#. \$\$ #   #. \$@ #   #. \$  #   #. \$  #   #. \$  #   #. \$  #   #. \$  #   #.\$@  #
#.\$\$  #   #.\$\$  #   #.\$\$  #   #.\$\$  #   #.\$\$  #   #.\$\$  #   #.\$\$  #   #.\$\$  #
#.#  @#   #.#   #   #.#   #   #.#   #   #.#   #   #.#   #   #.#   #   #.#   #
#######   #######   #######   #######   #######   #######   #######   #######

#######   #######   #######   #######   #######   #######   #######
#     #   #     #   #     #   #     #   #     #   #     #   #     #
#     #   #     #   #     #   #     #   #     #   #     #   #     #
#* #  #   #* #  #   #* #  #   #* #  #   #* #  #   #* #  #   #* #  #
#.\$\$  #   #.\$\$  #   #.@\$  #   #. \$  #   #.\$@  #   #*@   #   #*    #
#.\$@  #   #*@   #   #*\$   #   #+\$   #   #.\$   #   #.\$   #   #*@   #
#.#   #   #.#   #   #.#   #   #*#   #   #*#   #   #*#   #   #*#   #
#######   #######   #######   #######   #######   #######   #######
```

Other tests:

```constant input = """
#############
#  #        #
# \$\$\$\$\$\$\$  @#
#.......    #
#############
"""
```
Output:
```solution of 30 pushes (14.6s)
#############   #############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
# \$\$\$\$\$\$\$  @#   # @\$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #
#.......    #   #.*.....    #   #.+*....    #   #..+*...    #   #...+*..    #   #....+*.    #   #.....+*    #   #......+\$   #
#############   #############   #############   #############   #############   #############   #############   #############

#############   #############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
#  \$\$\$\$\$\$   #   #  \$\$\$\$\$\$   #   #  \$@\$\$\$\$   #   # \$@ \$\$\$\$   #   # @  \$\$\$\$   #   #    \$@\$\$   #   #   \$@ \$\$   #   #  \$@  \$\$   #
#.......@\$  #   #....... @\$ #   #...*...  \$ #   #...*...  \$ #   #.*.*...  \$ #   #.*.*.*.  \$ #   #.*.*.*.  \$ #   #.*.*.*.  \$ #
#############   #############   #############   #############   #############   #############   #############   #############

#############   #############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
# \$@   \$\$   #   #\$@    \$\$   #   #@     \$\$   #   #      \$@   #   #     \$@    #   #    \$@     #   #   \$@      #   #   \$       #
#.*.*.*.  \$ #   #.*.*.*.  \$ #   #**.*.*.  \$ #   #**.*.*.\$ \$ #   #**.*.*.\$ \$ #   #**.*.*.\$ \$ #   #**.*.*.\$ \$ #   #***+.*.\$ \$ #
#############   #############   #############   #############   #############   #############   #############   #############

#############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
#   @       #   #           #   #           #   #           #   #           #   #           #   #           #
#****.*.\$ \$ #   #*****+.\$ \$ #   #*****.*@ \$ #   #******+  \$ #   #******. \$@ #   #******.\$@  #   #*******@   #
#############   #############   #############   #############   #############   #############   #############
```

Test #3

```constant input = """
####
##. ##
##### .  #
#   #  # #
# \$ #  # #
# \$  @   #
######  ##
####
"""
```
Output:
```solution of 16 pushes (0.0s)
####         ####         ####         ####         ####         ####         ####         ####         ####
##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##
##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### *  #
#   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   # \$# #   #   # @# #
# \$ #  # #   # @\$#  # #   #  \$#  # #   #  \$#  # #   #  \$#  # #   #  \$#  # #   #  \$# \$# #   #  \$# @# #   #  \$#  # #
# \$  @   #   # \$      #   # @\$     #   #  @\$    #   #   @\$   #   #    @\$  #   #     @  #   #        #   #        #
######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##
####         ####         ####         ####         ####         ####         ####         ####         ####

####         ####         ####         ####         ####         ####         ####         ####
##* ##       ##* ##       ##* ##       ##* ##       ##* ##       ##* ##       ##* ##       ##* ##
##### +  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### *  #
#   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   # \$# #   #   # @# #
#  \$#  # #   #  @#  # #   #   #  # #   #   #  # #   #   #  # #   #   # \$# #   #   # @# #   #   #  # #
#        #   #  \$     #   #  @\$    #   #   @\$   #   #    @\$  #   #     @  #   #        #   #        #
######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##
####         ####         ####         ####         ####         ####         ####         ####
```

Test #4

```constant input = """
#############
#... #      #
#.\$\$\$\$\$\$\$  @#
#...        #
#############
"""
```
Output:
```"started"
solution of 40 pushes (58.5s)
#############   #############   #############   #############   #############   #############
#... #      #   #... #      #   #.*. #      #   #.** #      #   #.** #      #   #.** #      #
#.\$\$\$\$\$\$\$  @#   #.\$\$@\$\$\$\$   #   #.@\$ \$\$\$\$   #   #. @ \$\$\$\$   #   #.   \$\$\$\$   #   #.   \$\$\$\$   #
#...        #   #...\$       #   #...\$       #   #...\$       #   #...@\$      #   #... @\$     #
#############   #############   #############   #############   #############   #############
<snip 30 pushes>
#############   #############   #############   #############   #############
#*** #      #   #*** #      #   #*** #      #   #*** #      #   #*** #      #
#*          #   #*          #   #*          #   #*          #   #*          #
#**.   \$@   #   #**.  \$@    #   #**. \$@     #   #**.\$@      #   #***@       #
#############   #############   #############   #############   #############
```

Test #5

```constant input = """
#####
#   #
#   #
### #\$##
#      #
### #\$## #   ######
#   # ## #####   .#
# \$   \$         ..#
##### ### #@##   .#
#     #########
#######
"""
```
Output:
```solution of 59 pushes (25.5s)
#####                 #####                 #####                 #####
#   #                 #   #                 #   #                 #   #
#   #                 #   #                 #   #                 #   #
### #\$##              ### #@##              ### # ##              ### # ##
#      #              #    \$ #              #   \$@ #              #   \$  #
### #\$## #   ######   ### #\$## #   ######   ### #\$## #   ######   ### #@## #   ######
#   # ## #####   .#   #   # ## #####   .#   #   # ## #####   .#   #   #\$## #####   .#
# \$   \$         ..#   # \$   \$         ..#   # \$   \$         ..#   # \$   \$         ..#
##### ### #@##   .#   ##### ### # ##   .#   ##### ### # ##   .#   ##### ### # ##   .#
#     #########       #     #########       #     #########       #     #########
#######               #######               #######               #######

<snip 52 pushes>

#####                 #####                 #####                 #####
#   #                 #   #                 #   #                 #   #
#   #                 #   #                 #   #                 #   #
### # ##              ### # ##              ### # ##              ### # ##
#      #              #      #              #      #              #      #
### # ## #   ######   ### # ## #   ######   ### # ## #   ######   ### # ## #   ######
#   # ## #####   *#   #   # ## #####   *#   #   # ## #####   *#   #   # ## #####   *#
#             @\$.*#   #              @**#   #               **#   #               **#
##### ### # ## \$ .#   ##### ### # ## \$ .#   ##### ### # ## @\$.#   ##### ### # ##  @*#
#     #########       #     #########       #     #########       #     #########
#######               #######               #######               #######
```

## PicoLisp

This searches for a solution, without trying for the push-optimal one. The player moves between the pushes, however, are minimized.

```(load "@lib/simul.l")

# Display board
(de display ()
(disp *Board NIL
'((This)
(pack
(if2 (== This *Pos) (memq This *Goals)
"+"                   # Player on goal
"@"                   # Player elsewhere
(if (: val) "*" ".")  # On gloal
(or (: val) " ") )    # Elsewhere
" " ) ) ) )

# Initialize
(de main (Lst)
(mapc
'((B L)
(mapc
'((This C)
(case C
(" ")
("." (push '*Goals This))
("@" (setq *Pos This))
("\$" (=: val C) (push '*Boxes This))
(T (=: val C)) ) )
B L ) )
(setq *Board (grid (length (car Lst)) (length Lst)))
(apply mapcar (flip (mapcar chop Lst)) list) )
(display) )

# Generate possible push-moves
(de pushes ()
(make
(for Box *Boxes
(unless (or (; (west Box) val) (; (east Box) val))
(when (moves (east Box))
(link (cons (cons Box (west Box)) *Pos "L" @)) )
(when (moves (west Box))
(link (cons (cons Box (east Box)) *Pos "R" @)) ) )
(unless (or (; (south Box) val) (; (north Box) val))
(when (moves (north Box))
(link (cons (cons Box (south Box)) *Pos "D" @)) )
(when (moves (south Box))
(link (cons (cons Box (north Box)) *Pos "U" @)) ) ) ) ) )

# Moves of player to destination
(de moves (Dst Hist)
(or
(== Dst *Pos)
(mini length
(extract
'((Dir)
(with ((car Dir) Dst)
(cond
((== This *Pos) (cons (cdr Dir)))
((: val))
((memq This Hist))
((moves This (cons Dst Hist))
(cons (cdr Dir) @) ) ) ) )
'((west . "r") (east . "l") (south . "u") (north . "d")) ) ) ) )

# Find solution
(de go (Res)
(unless (idx '*Hist (sort (copy *Boxes)) T)  # No repeated state
(if (find '((This) (<> "\$" (: val))) *Goals)
(pick
'((Psh)
(setq  # Move
*Pos (caar Psh)
*Boxes (cons (cdar Psh) (delq *Pos *Boxes)) )
(put *Pos 'val NIL)
(put (cdar Psh) 'val "\$")
(prog1 (go (append (cddr Psh) Res))
(setq  # Undo move
*Boxes (cons (caar Psh) (delq (cdar Psh) *Boxes)) )
(put (cdar Psh) 'val NIL)
(put (caar Psh) 'val "\$") ) )
(pushes) )
(display)  # Display solution
(pack (flip Res)) ) ) )```

Test:

```(main
(quote
"#######"
"#     #"
"#     #"
"#. #  #"
"#. \$\$ #"
"#.\$\$  #"
"#.#  @#"
"#######" ) )
(prinl)
(go)```

Output:

``` 8 # # # # # # #
7 #           #
6 #           #
5 # .   #     #
4 # .   \$ \$   #
3 # . \$ \$     #
2 # . #     @ #
1 # # # # # # #
a b c d e f g

8 # # # # # # #
7 #           #
6 # @         #
5 # *   #     #
4 # *         #
3 # *         #
2 # * #       #
1 # # # # # # #
a b c d e f g
-> "uuulDLLulDDurrrrddlUruLLLrrddlUruLdLUUdrruulLulD"```

## Python

Translation of: D
Works with: Psyco
Works with: Python 2.6
```from array import array
from collections import deque
import psyco

data = []
nrows = 0
px = py = 0
sdata = ""
ddata = ""

def init(board):
global data, nrows, sdata, ddata, px, py
data = filter(None, board.splitlines())
nrows = max(len(r) for r in data)

maps = {' ':' ', '.': '.', '@':' ', '#':'#', '\$':' '}
mapd = {' ':' ', '.': ' ', '@':'@', '#':' ', '\$':'*'}

for r, row in enumerate(data):
for c, ch in enumerate(row):
sdata += maps[ch]
ddata += mapd[ch]
if ch == '@':
px = c
py = r

def push(x, y, dx, dy, data):
if sdata[(y+2*dy) * nrows + x+2*dx] == '#' or \
data[(y+2*dy) * nrows + x+2*dx] != ' ':
return None

data2 = array("c", data)
data2[y * nrows + x] = ' '
data2[(y+dy) * nrows + x+dx] = '@'
data2[(y+2*dy) * nrows + x+2*dx] = '*'
return data2.tostring()

def is_solved(data):
for i in xrange(len(data)):
if (sdata[i] == '.') != (data[i] == '*'):
return False
return True

def solve():
open = deque([(ddata, "", px, py)])
visited = set([ddata])
dirs = ((0, -1, 'u', 'U'), ( 1, 0, 'r', 'R'),
(0,  1, 'd', 'D'), (-1, 0, 'l', 'L'))

lnrows = nrows
while open:
cur, csol, x, y = open.popleft()

for di in dirs:
temp = cur
dx, dy = di[0], di[1]

if temp[(y+dy) * lnrows + x+dx] == '*':
temp = push(x, y, dx, dy, temp)
if temp and temp not in visited:
if is_solved(temp):
return csol + di[3]
open.append((temp, csol + di[3], x+dx, y+dy))
else:
if sdata[(y+dy) * lnrows + x+dx] == '#' or \
temp[(y+dy) * lnrows + x+dx] != ' ':
continue

data2 = array("c", temp)
data2[y * lnrows + x] = ' '
data2[(y+dy) * lnrows + x+dx] = '@'
temp = data2.tostring()

if temp not in visited:
if is_solved(temp):
return csol + di[2]
open.append((temp, csol + di[2], x+dx, y+dy))

return "No solution"

level = """\
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######"""

psyco.full()
init(level)
print level, "\n\n", solve()
```

Output:

```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## Racket

This was originally inspired by PicoLisp's solution. Modified to use a priority queue as mentioned on the Sokoban wiki for the main breadth first search on pushes but just a plain queue for the move bfs. This uses personal libraries. Vector2 isn't strictly needed but the math/array library is not currently optimized for untyped Racket. push! is comparable to lisp's, awhen is anaphoric when, ret uses the bound value as the result of its expression, and tstruct is short for struct with the #:transparent option.

```#lang racket
(require data/heap
"../lib/vector2.rkt" "../lib/queue.rkt" (only-in "../lib/util.rkt" push! tstruct ret awhen))

(define level (list "#######"
"#     #"
"#     #"
"#. #  #"
"#. \$\$ #"
"#.\$\$  #"
"#.#  @#"
"#######"))
(define (strings->vec2 l) (lists->vec2 (map string->list l)))
;turn everything except walls into distance from goals
(define (clear-level l)
(ret ([l (vec2-copy l)])
(define dots (vec2-atsq l #\.))
(define q (list->q (map (λ (p) (cons p 0)) dots)))
(let bfs () ;this search has implicit history in the mutated vector2
(unless (nilq? q)
(match-define (cons p n) (deq! q))
(define x (vec2@ l p))
;stop if position is either a wall or a previously filled number
(cond [(or (eq? x #\#) (number? x)) (bfs)]
[else (vec2! l p n)
(for-adj l x [p p] #f (enq! (cons p (add1 n)) q))
(bfs)])))))

;corresponds to PicoLisp's move table in "moves", while also adding a push direction mapping
(tstruct move (f d))
(define-values (mu md ml mr LURD)
(let ()
(define t (map (λ (x) (cons (car x) (apply pos (cdr x))))
'([#\u -1 0] [#\d 1 0] [#\l 0 -1] [#\r 0 1])))
(define (mv d)
(define x (assoc d t))
(move (λ (p) (pos+ p (cdr x))) (car x)))
(values (mv #\u) (mv #\d) (mv #\l) (mv #\r)
(λ (d) (char-upcase (car (findf (λ (x) (equal? d (cdr x))) t)))))))

;state = player pos * box poses
(tstruct st (p b))
(define (st= s1 s2) (andmap (λ (b) (member b (st-b s2))) (st-b s1)))
(define (box? p s) (member p (st-b s)))
;calculates value of a state for insertion into priority queue
;value is sum of box distances from goals
(define (value s l) (apply + (map (λ (p) (vec2@ l p)) (st-b s))))
;init state for a level
(define (st0 l) (st (vec2-atq l #\@) (vec2-atsq l #\\$)))
(define (make-solution-checker l)
(define dots (vec2-atsq l #\.))
(λ (s) (andmap (λ (b) (member b dots)) (st-b s))))

;state after push * lurd history
(tstruct push (st h))
(define (pushes s l)
(ret ([pushes '()])
(for ([b (in-list (st-b s))])
(for-adj l a [p b] #f
(define d (pos- p b)) ;direction of push
(define op (pos- b d)) ;where player stands to push
(define o (vec2@ l op))
;make sure push pos and push dest are clear
(when (and (number? a) (number? o)
(not (box? p s)) (not (box? op s)))
(awhen [@ (moves s op l)]
(define new-st (st b (cons p (remove b (st-b s)))))
(push! (push new-st (cons (LURD d) @)) pushes)))))))

;state * goal pos * level -> lurd string
(define (moves s g l)
(define h '())
(define q (list->q (list (list (st-p s)))))
(let bfs ()
(if (nilq? q)
#f
(match-let ([(cons p lurd) (deq! q)])
(cond [(equal? p g) lurd]
[(or (char=? (vec2@ l p) #\#) (box? p s) (member p h)) (bfs)]
[else (push! p h)
(for-each (λ (m)
(match-define (move f s) m)
(enq! (cons (f p) (cons s lurd)) q))
(list mu md ml mr))
(bfs)])))))

(define (sokoban l)
(define-values (clear s0 solved?)
(let ([l (strings->vec2 l)])
(values (clear-level l) (st0 l) (make-solution-checker l))))
(define h '())
(tstruct q-elem (s lurd v)) ;priority queue stores state, lurd hist, and value
(define (elem<= s1 s2) (<= (q-elem-v s1) (q-elem-v s2))) ;compare wrapped values
;queue stores a single element at the beginning consisting of:
;1. starting state, 2. empty lurd history, 3. value of starting state
(define q (vector->heap elem<= (vector (q-elem s0 '() (value s0 clear)))))
(let bfs ()
(match-define (q-elem s lurd _) (heap-min q))
(heap-remove-min! q)
(cond [(solved? s) (list->string (reverse lurd))]
[(memf (λ (s1) (st= s s1)) h) (bfs)]
[else (push! s h)
(for-each (λ (p)
(define s (push-st p))
(heap-add! q (q-elem s (append (push-h p) lurd) (value s clear))))
(pushes s clear))
(bfs)])))
```
Output:

Times shown are milliseconds.

```> (time (sokoban level))
cpu time: 88 real time: 83 gc time: 0
"uuulDLLrrrddllUdrruulLrrdLuuulldlDDuuurrrddlLrrddlULrruLdlUUdrruulLulD"
```

## Raku

(formerly Perl 6)

Translation of: Go
```sub MAIN() {
my \$level = q:to//;
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

say 'level:';
print \$level;
say 'solution:';
say solve(\$level);
}

class State {
has Str \$.board;
has Str \$.sol;
has Int \$.pos;

method move(Int \$delta --> Str) {
my \$new = \$!board;
if \$new.substr(\$!pos,1) eq '@' {
substr-rw(\$new,\$!pos,1) = ' ';
} else {
substr-rw(\$new,\$!pos,1) = '.';
}
my \$pos := \$!pos + \$delta;
if \$new.substr(\$pos,1) eq ' ' {
substr-rw(\$new,\$pos,1) = '@';
} else {
substr-rw(\$new,\$pos,1) = '+';
}
return \$new;
}

method push(Int \$delta --> Str) {
my \$pos := \$!pos + \$delta;
my \$box := \$pos + \$delta;
return '' unless \$!board.substr(\$box,1) eq ' ' | '.';
my \$new = \$!board;
if \$new.substr(\$!pos,1) eq '@' {
substr-rw(\$new,\$!pos,1) = ' ';
} else {
substr-rw(\$new,\$!pos,1) = '.';
}
if \$new.substr(\$pos,1) eq '\$' {
substr-rw(\$new,\$pos,1) = '@';
} else {
substr-rw(\$new,\$pos,1) = '+';
}
if \$new.substr(\$box,1) eq ' ' {
substr-rw(\$new,\$box,1) = '\$';
} else {
substr-rw(\$new,\$box,1) = '*';
}
return \$new;
}
}

sub solve(Str \$start --> Str) {
my \$board = \$start;
my \$width = \$board.lines[0].chars + 1;
my @dirs =
["u", "U", -\$width],
["r", "R", 1],
["d", "D", \$width],
["l", "L", -1];

my %visited = \$board => True;

my \$pos = \$board.index('@');
my @open = State.new(:\$board, :sol(''), :\$pos);
while @open {
my \$state = @open.shift;
for @dirs -> [\$move, \$push, \$delta] {
my \$board;
my \$sol;
my \$pos = \$state.pos + \$delta;
given \$state.board.substr(\$pos,1) {
when '\$' | '*' {
\$board = \$state.push(\$delta);
next if \$board eq "" || %visited{\$board};
\$sol = \$state.sol ~ \$push;
return \$sol unless \$board ~~ /<[ . + ]>/;
}
when ' ' | '.' {
\$board = \$state.move(\$delta);
next if %visited{\$board};
\$sol = \$state.sol ~ \$move;
}
default { next }
}
@open.push: State.new: :\$board, :\$sol, :\$pos;
%visited{\$board} = True;
}
}
return "No solution";
}
```
Output:
```Level:
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
Solution:
ulULLulDDurrrddlULrruLLrrUruLLLulD```

## Ring

```#--------------------------------------------------#
# Sokoban Game  				   #
#--------------------------------------------------#

# Game Data

aPlayer = [ :Row = 3, :Col = 4 ]

aLevel1 = [
[1,1,1,2,2,2,2,2,1,1,1,1,1,1],
[1,2,2,2,1,1,1,2,1,1,1,1,1,1],
[1,2,4,3,5,1,1,2,1,1,1,1,1,1],
[1,2,2,2,1,5,4,2,1,1,1,1,1,1],
[1,2,4,2,2,5,1,2,1,1,1,1,1,1],
[1,2,1,2,1,4,1,2,2,1,1,1,1,1],
[1,2,5,1,6,5,5,4,2,1,1,1,1,1],
[1,2,1,1,1,4,1,1,2,1,1,1,1,1],
[1,2,2,2,2,2,2,2,2,1,1,1,1,1],
[1,1,1,1,1,1,1,1,1,1,1,1,1,1]
]

aLevel2 = [
[1,1,1,2,2,2,2,2,2,2,2,2,1,1],
[1,2,2,2,1,5,1,4,1,1,1,2,1,1],
[1,2,4,3,5,1,1,1,5,1,1,2,1,1],
[1,2,2,2,1,1,4,1,1,1,1,2,1,1],
[1,2,4,2,2,1,5,4,1,5,1,2,1,1],
[1,2,1,2,1,4,1,5,1,1,2,2,1,1],
[1,2,5,1,6,5,1,4,1,1,1,2,1,1],
[1,2,1,1,1,4,1,4,1,5,1,2,1,1],
[1,2,2,2,2,2,2,2,2,2,2,2,1,1],
[1,1,1,1,1,1,1,1,1,1,1,1,1,1]
]

aLevel = aLevel1
nActiveLevel = 1

# For Game Restart
aLevel1Copy  = aLevel1
aLevel2Copy  = aLevel2
aPlayerCopy = aPlayer

C_LEVEL_ROWSCOUNT = 10
C_LEVEL_COLSCOUNT = 14

C_EMPTY 	= 1
C_WALL  	= 2
C_PLAYER	= 3
C_DOOR  	= 4
C_BOX   	= 5
C_BOXONDOOR 	= 6
C_PLAYERONDOOR  = 7

nKeyClock = clock()

# Will be used when moving a Box
aCurrentBox = [ :Row = 0, :Col = 0 ]
nRowDiff = 0
nColDiff = 0

# When the player win
lPlayerWin = False

func main

oGame = New Game
{

title = "Sokoban"

Map {

blockwidth  = 60
blockheight = 60

aMap = aLevel

aImages = [
"images/empty.jpg",
"images/wall.jpg",
"images/player.jpg",
"images/door.jpg",
"images/box.jpg",
"images/boxondoor.jpg",
"images/player.jpg"	# Player on Door
]

keypress = func oGame,oSelf,nkey {
# Avoid getting many keys in short time
if (clock() - nKeyClock) < clockspersecond()/4 return ok
nKeyClock = Clock()
Switch nkey
on Key_Esc
oGame.Shutdown()
on Key_Space
# Restart the Level
if nActiveLevel = 1
aLevel = aLevel1Copy
else
aLevel = aLevel2Copy
ok
aPlayer = aPlayerCopy
UpdateGameMap(oGame)
lPlayerWin = False
on Key_Right
if aPlayer[:col] < C_LEVEL_COLSCOUNT
nRowDiff = 0   nColDiff = 1
MoveObject(oGame,PlayerType(),aPlayer[:row],aPlayer[:col]+1)
ok
on Key_Left
if aPlayer[:col] > 1
nRowDiff = 0   nColDiff = -1
MoveObject(oGame,PlayerType(),aPlayer[:row],aPlayer[:col]-1)
ok
on Key_Up
if aPlayer[:row] > 1
nRowDiff = -1   nColDiff = 0
MoveObject(oGame,PlayerType(),aPlayer[:row]-1,aPlayer[:col])
ok
on Key_Down
if aPlayer[:row] < C_LEVEL_ROWSCOUNT
nRowDiff = 1   nColDiff = 0
MoveObject(oGame,PlayerType(),aPlayer[:row]+1,aPlayer[:col])
ok
off
if lPlayerWin = False
if CheckWin()
lPlayerWin = True
DisplayYouWin(oGame)
ok
ok
}

}

text {
x = 70	y=550
animate = false
size = 20
file = "fonts/pirulen.ttf"
text = "Level:"
color = rgb(0,0,0)
}
NewButton(oGame,180,550,150,30,"Level 1",:Click1)
NewButton(oGame,350,550,150,30,"Level 2",:Click2)
}

func MoveObject oGame,nObjectType,nNewRow,nNewCol
lMove = False
switch nObjectType
on  C_PLAYER
switch aLevel[nNewRow][nNewCol]
on C_EMPTY
aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_PLAYER
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
on C_DOOR
aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_PLAYERONDOOR
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
on C_BOX
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff)
aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_PLAYER
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
ok
on C_BOXONDOOR
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff)
aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_PLAYERONDOOR
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
ok
off
on  C_PLAYERONDOOR
switch aLevel[nNewRow][nNewCol]
on C_EMPTY
aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_PLAYER
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
on C_DOOR
aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_PLAYERONDOOR
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
on C_BOX
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff)
aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_PLAYER
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
ok
on C_BOXONDOOR
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff)
aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_PLAYER
UpdateGameMap(oGame)
aPlayer[:row] = nNewRow
aPlayer[:col] = nNewCol
lMove = True
ok
off
on  C_BOX
switch aLevel[nNewRow][nNewCol]
on C_EMPTY
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_BOX
UpdateGameMap(oGame)
lMove = True
on C_DOOR
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_BOXONDOOR
UpdateGameMap(oGame)
lMove = True
on C_BOX
aOldBox = aCurrentBox
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff)
aCurrentBox = aOldBox
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_BOX
UpdateGameMap(oGame)
lMove = True
ok
on C_BOXONDOOR
aOldBox = aCurrentBox
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff)
aCurrentBox = aOldBox
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY
aLevel[nNewRow][nNewCol] = C_BOXONDOOR
UpdateGameMap(oGame)
lMove = True
ok
off
on  C_BOXONDOOR
switch aLevel[nNewRow][nNewCol]
on C_EMPTY
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_BOX
UpdateGameMap(oGame)
lMove = True
on C_DOOR
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_BOXONDOOR
UpdateGameMap(oGame)
lMove = True
on C_BOX
aOldBox = aCurrentBox
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff)
aCurrentBox = aOldBox
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_BOX
UpdateGameMap(oGame)
lMove = True
ok
on C_BOXONDOOR
aOldBox = aCurrentBox
aCurrentBox[:row] = nNewRow
aCurrentBox[:col] = nNewCol
if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff)
aCurrentBox = aOldBox
aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR
aLevel[nNewRow][nNewCol] = C_BOXONDOOR
UpdateGameMap(oGame)
lMove = True
ok

off
off
return lMove

func UpdateGameMap oGame
# The Map is our first object in Game Objects
oGame.aObjects[1].aMap = aLevel

func PlayerType
# It could be (Player) or (Player on door)
return aLevel[aPlayer[:row]][aPlayer[:col]]

func CheckWin
for aRow in aLevel
if find(aRow,C_DOOR) or find(aRow,C_PLAYERONDOOR)
return False
ok
next
return True

func DisplayYouWin oGame
oGame {
text {
point = 400
size = 30
nStep = 9
file = "fonts/pirulen.ttf"
text = "You Win !!!"
x = 500  y=10
state = func ogame,oself {
if oself.y >= 400
ogame.remove(oSelf.nIndex)
ok
}
}
}

func NewButton oGame,nX,nY,nWidth,nHeight,cText,cFunc
oGame {
Object {
x = nX y=nY width = nWidth height=nHeight
Text = cText
EventCode = cFunc
draw = func oGame,oSelf {
oSelf {
gl_draw_filled_rectangle(x,y,x+width,y+height,gl_map_rgb(0,100,255))
gl_draw_rectangle(x,y,x+width,y+height,gl_map_rgb(0,0,0),2)
gl_draw_text(oFont,gl_map_rgb(0,0,0),x+width/2,y+5,1,Text)
}
}
mouse = func oGame,oSelf,nType,aMouseList {
if nType = GE_MOUSE_UP
MouseX = aMouseList[GE_MOUSE_X]
MouseY = aMouseList[GE_MOUSE_Y]
oSelf {
if MouseX >= x and MouseX <= X+270 and
MouseY >= y and MouseY <= Y+40
call EventCode(oGame,oSelf)
ok
}
ok
}
}
}
return len(oGame.aObjects)

func Click1 oGame,oSelf
aLevel = aLevel1
nActiveLevel = 1
aPlayer = aPlayerCopy
UpdateGameMap(oGame)
lPlayerWin = False

func Click2 oGame,oSelf
aLevel = aLevel2
nActiveLevel = 2
aPlayer = aPlayerCopy
UpdateGameMap(oGame)
lPlayerWin = False```

Output image:

## Ruby

### Simple Version

Translation of: Python
```require 'set'

class Sokoban
def initialize(level)
board = level.each_line.map(&:rstrip)
@nrows = board.map(&:size).max
board.map!{|line| line.ljust(@nrows)}
board.each_with_index do |row, r|
row.each_char.with_index do |ch, c|
@px, @py = c, r  if ch == '@' or ch == '+'
end
end
@goal = board.join.tr(' .@#\$+*', ' .   ..')
.each_char.with_index.select{|ch, c| ch == '.'}
.map(&:last)
@board = board.join.tr(' .@#\$+*', '  @#\$ \$')
end

def pos(x, y)
y * @nrows + x
end

def push(x, y, dx, dy, board)         # modify board
return  if board[pos(x+2*dx, y+2*dy)] != ' '
board[pos(x     , y     )] = ' '
board[pos(x + dx, y + dy)] = '@'
board[pos(x+2*dx, y+2*dy)] = '\$'
end

def solved?(board)
@goal.all?{|i| board[i] == '\$'}
end

DIRS = [[0, -1, 'u', 'U'], [ 1, 0, 'r', 'R'], [0,  1, 'd', 'D'], [-1, 0, 'l', 'L']]
def solve
queue = [[@board, "", @px, @py]]
visited = Set[@board]

until queue.empty?
current, csol, x, y = queue.shift

for dx, dy, cmove, cpush in DIRS
work = current.dup
case work[pos(x+dx, y+dy)]      # next character
when '\$'
next  unless push(x, y, dx, dy, work)
return csol+cpush  if solved?(work)
queue << [work, csol+cpush, x+dx, y+dy]
when ' '
work[pos(x, y)]       = ' '
work[pos(x+dx, y+dy)] = '@'
queue << [work, csol+cmove, x+dx, y+dy]  if visited.add?(work)
end
end
end
"No solution"
end
end
```

Test:

```level = <<EOS
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
EOS
puts level, "", Sokoban.new(level).solve
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD
```

### Faster Version

It examines beforehand the place where the box can not move to the goal. When a box is pushed there, it doesn't process after that.

```class Sokoban
def initialize(level)
board = level.lines.map(&:rstrip)
leng  = board.map(&:length).max
board = board.map{|line| line.ljust(leng)}.join
@goal = []
board.each_char.with_index do |c, i|
@player = i  if c == '@' or c == '+'
@goal << i   if c == '.' or c == '+' or c == '*'
end
@board = board.tr(' .@#\$+*', '  @#\$ \$')
@lurd = [[-1, 'l', 'L'], [-leng, 'u', 'U'], [1, 'r', 'R'], [leng, 'd', 'D']]
@dirs = @lurd.map(&:first)
end

corner = search_corner(wall)
begin
corner.each do |pos|
@dirs.each do |dir|
next  if wall[pos + dir] == '#'
end
end
end

def search_corner(wall)
wall.size.times.with_object([]) do |i, corner|
next  if wall[i] == '#' or @goal.include?(i)
case count_wall(wall, i)
when 2
corner << i  if wall[i-1] != wall[i+1]
when 3
corner << i
end
end
end

def check_side(wall, pos, dir)
wk = []
until wall[pos] == '#' or count_wall(wall, pos) == 0 or @goal.include?(pos)
wk << pos
pos += dir
end
[]
end

def count_wall(wall, pos)
@dirs.count{|dir| wall[pos + dir] == '#'}
end

def push_box(pos, dir, board)
return board  if board[pos + 2*dir] != ' '
board[pos        ] = ' '
board[pos +   dir] = '@'
board[pos + 2*dir] = '\$'
board
end

def solved?(board)
@goal.all?{|i| board[i] == '\$'}
end

def solve
queue = [[@board, "", @player]]
# When the key doesn't exist in Hash, it subscribes a key but it returns false.
visited = Hash.new{|h,k| h[k]=true; false}
visited[@board]                     # first subscription

until queue.empty?
board, route, pos = queue.shift
@lurd.each do |dir, move, push|
work = board.dup
case work[pos+dir]
when '\$'    # push
work = push_box(pos, dir, work)
next  if visited[work]
return route+push  if solved?(work)
queue << [work, route+push, pos+dir]  unless @dead.include?(pos+2*dir)
when ' '    # move
work[pos    ] = ' '
work[pos+dir] = '@'
next  if visited[work]
queue << [work, route+move, pos+dir]
end
end
end
"No solution"
end
end
```

## Tcl

This code does a breadth-first search so it finds a solution with a minimum number of moves.

Translation of: OCaml
```package require Tcl 8.5

proc solveSokoban b {
set cols [string length [lindex \$b 0]]
set dxes [list [expr {-\$cols}] \$cols -1 1]
set i 0
foreach c [split [join \$b ""] ""] {
switch \$c {
" " {lappend bdc " "}
"#" {lappend bdc "#"}
"@" {lappend bdc " ";set startplayer \$i }
"\$" {lappend bdc " ";lappend startbox \$i}
"." {lappend bdc " ";                    lappend targets \$i}
"+" {lappend bdc " ";set startplayer \$i; lappend targets \$i}
"*" {lappend bdc " ";lappend startbox \$i;lappend targets \$i}
}
incr i
}
set q [list [list \$startplayer \$startbox] {}]
set store([lindex \$q 0]) {}
for {set idx 0} {\$idx < [llength \$q]} {incr idx 2} {
lassign [lindex \$q \$idx] x boxes
foreach dir {U D L R} dx \$dxes {
if {[set x1 [expr {\$x + \$dx}]] in \$boxes} {
if {[lindex \$bdc [incr x1 \$dx]] ne " " || \$x1 in \$boxes} {
continue
}
set tmpboxes \$boxes
set x1 [expr {\$x + \$dx}]
for {set i 0} {\$i < [llength \$boxes]} {incr i} {
if {[lindex \$boxes \$i] == \$x1} {
lset tmpboxes \$i [expr {\$x1 + \$dx}]
break
}
}
if {\$dx == 1 || \$dx == -1} {
set next [list \$x1 \$tmpboxes]
} else {
set next [list \$x1 [lsort -integer \$tmpboxes]]
}
if {![info exists store(\$next)]} {
if {\$targets eq [lindex \$next 1]} {
foreach c [lindex \$q [expr {\$idx + 1}]] {
lassign \$c ispush olddir
if {\$ispush} {
append solution \$olddir
} else {
append solution [string tolower \$olddir]
}
}
return [append solution \$dir]
}
set store(\$next) {}
set nm [lindex \$q [expr {\$idx + 1}]]
lappend q \$next
lappend q [lappend nm [list 1 \$dir]]
}
} elseif {[lindex \$bdc \$x1] eq " "} {
set next [list [expr {\$x + \$dx}] \$boxes]
if {![info exists store(\$next)]} {
set store(\$next) {}
set nm [lindex \$q [expr {\$idx + 1}]]
lappend q \$next
lappend q [lappend nm [list 0 \$dir]]
}
}
}
}
error "no solution"
}
```

Demonstration code:

```set level {
"#######"
"#     #"
"#     #"
"#. #  #"
"#. \$\$ #"
"#.\$\$  #"
"#.#  @#"
"#######"
}
puts [solveSokoban \$level]
```

Output:

`ulULLulDDurrrddlULrruLLrrUruLLLulD`

Runtime with stock Tcl 8.5 installation: ≅2.2 seconds

## Wren

Translation of: Kotlin
Library: Wren-dynamic
Library: Wren-llist
Library: Wren-set

This works but at a rather sedate pace - 26.7 seconds.

```import "./dynamic" for Tuple
import "./set" for Set

var Board = Tuple.create("Board", ["cur", "sol", "x", "y"])

class Sokoban {
construct new(board) {
_destBoard = ""
_currBoard = ""
_nCols = board[0].count
_playerX = 0
_playerY = 0
for (r in 0...board.count) {
for (c in 0..._nCols) {
var ch = board[r][c]
_destBoard = _destBoard + ((ch != "\$" && ch != "@") ? ch : " ")
_currBoard = _currBoard + ((ch != ".") ? ch : " ")
if (ch == "@") {
_playerX = c
_playerY = r
}
}
}
}

move(x, y, dx, dy, trialBoard) {
var newPlayerPos = (y + dy) * _nCols  + x + dx
if (trialBoard[newPlayerPos] != " ") return ""
var trial = trialBoard.toList
trial[y * _nCols + x] = " "
trial[newPlayerPos] = "@"
return trial.join()
}

push(x, y, dx, dy, trialBoard) {
var newBoxPos = (y + 2 * dy) * _nCols + x + 2 * dx
if (trialBoard[newBoxPos] != " ") return ""
var trial = trialBoard.toList
trial[y * _nCols + x] = " "
trial[(y + dy) * _nCols + x + dx] = "@"
trial[newBoxPos] = "\$"
return trial.join("")
}

isSolved(trialBoard) {
for (i in 0...trialBoard.count) {
if ((_destBoard[i] == ".") != (trialBoard[i] == "\$")) return false
}
return true
}

solve() {
var dirLabels = [ ["u", "U"], ["r", "R"], ["d", "D"], ["l", "L"] ]
var dirs = [ [0, -1], [1, 0], [0, 1], [-1, 0] ]
var history = Set.new()

while (!open.isEmpty) {
var b = open.removeAt(0)
for (i in 0...dirs.count) {
var trial = b.cur
var dx = dirs[i][0]
var dy = dirs[i][1]

// are we standing next to a box ?
if (trial[(b.y + dy) * _nCols + b.x + dx] == "\$") {
// can we push it ?
trial = push(b.x, b.y, dx, dy, trial)
if (!trial.isEmpty) {
// or did we already try this one ?
if (!history.contains(trial)) {
var newSol = b.sol + dirLabels[i][1]
if (isSolved(trial)) return newSol
open.add(Board.new(trial, newSol, b.x + dx, b.y + dy))
}
}
} else { // otherwise try changing position
trial = move(b.x, b.y, dx, dy, trial)
if (!trial.isEmpty && !history.contains(trial)) {
var newSol = b.sol + dirLabels[i][0]
open.add(Board.new(trial, newSol, b.x + dx, b.y + dy))
}
}
}
}
return "No solution"
}
}

var level = [
"#######",
"#     #",
"#     #",
"#. #  #",
"#. \$\$ #",
"#.\$\$  #",
"#.#  @#",
"#######"
]
System.print(level.join("\n"))
System.print()
System.print(Sokoban.new(level).solve())
```
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD
```